My first controller was a DDJ 200 and I felt that I was ready to upgrade. Wanna share anything I can that may help someone that was in my situation that may not know. As my budget was pretty tight, it came down to either this, or the REV-1. So here are my thoughts on a few different aspects.Software compatibility:The thing is, even though this controller is labeled as a Serato controller, its really much more primarily a Rekordbox controller.(I knew this and got it for Rekordbox but wanted to try Serato anyway to see what it was like.) No matter what I tried after several hours of troubleshooting, I was not able to get it to work correctly. It only worked one time, but that was it. There was also some latency with my inputs, like changing the volume fader or scratching etc. (could have been my USB cable. It also only worked with the lite edition, and not pro. Never did anything at all on pro, and pretty soon, never did anything on Lite either. Opened Rekordbox, as soon as I resolved an issue (will talk about in a minute) it worked great. Get Rekordbox if you want to use this controller. Or if you are using another controller that also used rekordbox like a ddj 200 400 etc. Especially since most of Rekordbox is usable without paying extra with this controller. Unlike serato lite, which limits the cue points, you cannot make playlists, you cant change key, and are limited to certain FX. etc. For that, you would need to pay 10$ a month for or a 250$ one time payment (sometimes its on sale for less) If Serato is something you're more familiar with/prefer and are willing to pay a subscription, get the Numark Mixtrack Platinum FX or the DDJ REV-1 as those are dedicated serato controllers and would work better if you prefer serato DJ lite or pro. Otherwise, Use this controller on Rekordbox and everything works as intended and is much less of a headache.Controller Itself:The controller itself is a huge upgrade from the DDJ 200, and I can see why it replaced the 400 as the golden standard of DJ controllers. It has a club style layout. Suited to playing EDM and Dance music. Though of course this can be done with any layout. The jog wheels are bigger as well, with a matte finish. They feel nice. not much complaint there. One thing I have a gripe about this controller with is the to engage FX, which is toggling a switch to either deck 1 or deck 2, and then hitting the FX button. Not too big a deal, but I really prefer having the FX paddles like on the REV-1 or on the Numark. As then you dont have to remember to toggle it back and forth between decks and shut it off by pressing the button again, but then rather you just flick the switch on the left side or right side for however long you want the FX on. Easier workflow if you ask me but its no big deal and I can get used to it. It has loop buttons on the top which allow you to instantly make loops to hype up the next song which is cool. The build quality feels decent too. Pressing the performance pads and moving/scratching the jog wheels feels satisfying. The volume faders and the cross faders feel decent too. It also has 2 unique buttons that are an "upgrade" over the DDJ 400. The smart fader and the smart cfx. I say "upgrade" in quotes because these buttons can be pretty polarizing topics. The smart CFX from what I can tell is really cool. Its basically a combination of multiple effects into one of the CFX knobs. You can also change the type of smart CFX by pressing "Shift" Together with the "Smart CFX" Button. They sound pretty cool and can spice up your transitions or music! I still think the original FX are better to use, but using these as a surprise to the audience once in a while could be cool! The... other addition unique to this controller is the smart fader... This... can be up for debate. Essentially, it automatically beat matches two songs and will automatically apply FX as you are transitioning from one song to the next. The good thing about it is that it can seemingly transition two wildly different genres and BPMS somewhat smoothly. The bad thing is that it sort of feels like a gimmick to me. As something like this will never replace good song selection, preparation, and mixing skills. Especially since its the only controller that I know of to have this feature. If you upgraded to a different one and you rely on this feature, youre on your own.My issue I hadI dont think anyone will experience the same issue, i was an idiot on this one, but in case, I will share. Rekordbox essentially told me that this controller could only be used if I had a paid plan. Was the first I heard of it. So I went ahead and got the paid plan. Thinking that would fix it, but it didnt. It unlocked Rekordbox, but it had no function whatsoever. No playing, no volume faders, loading songs, no nothing. The thing is though, that this unit is on the hardware unlock list, meaning that it SHOULD be free to perform with. But Rekordbox detected it as being the FLX4, so I had no idea what was going on... Until I realized that my Rekordbox was out of date... after I updated, everything worked perfectly. And I was able to cancel the paid plan. Moral of the story, update Rekordbox when you get this unit. If youre installing it for the first time, youre probably good. (Screenshots are of the issue I had and the hardware unlock list)Conclusion: As far as actually using the FLX4, I love it! Its loads of fun to DJ with. And I'd highly recommend this unit. I would recommend this controller over the REV-1 and the Numark if you are not willing to pay a subscription for serato dj pro. Especially since other then the FLX6, its the only Rekordbox controller available on amazon at the time of writing this, aka, the only controllers you wont be coaxed into paying monthly for. This controller is a blast to use and could totally see my self getting a club dancing with this! I would recommend the REV-1 and the Numark over this controller, if you prefer serato and are willing to pay monthly, or the REV-1 specifically if you value scratching and turntablism as its jog wheels are bigger, it has paddle FX, and its geared more towards scratching vs getting a club dancing. though it can actually do the exact same things, just laid out differently.