I would possibly suggest a Pioneer controller instead, especially if they think they might ever DJ in a bar/club. Honestly most of their line up looks pretty good for a beginner so you can probably choose on price, but feel free to post a few options and I can share my thoughts. e.g. this DDJ-FLX4 looks fine to me, or a second hand DDJ-400.
The reason for this is that pretty much every venue (in Europe at least? I assume it’s the same elsewhere) has Pioneer CDJs, it’s what every DJ uses in the house/techno world for example, and so if you use a Pioneer controller with their Rekordbox software, your song library is already in a format which you can just export to a USB stick and load into a CDJ with no problems if you did play a party. All your tags, folders, cue points etc. will be exactly as they are at home.
Also, the layout of the controllers is pretty similar to the real Pioneer CDJ/DJM mixer setup, so they would be able to hit the ground running with the “real” kit… and it’s the industry standard layout for a reason I guess.
The downside is that the Rekordbox software is not amazing. It’s fine, but the interface could be clearer etc. However, Traktor is also feeling pretty old fashioned (at least it was when I last used it), so I’m not sure if this is a huge differentiator, and if you ever want to use CDJs, Rekordbox is a necessary evil as it’s the only way to curate your library.
There are other alternatives which are interesting for sure, but I think Pioneer’s dominance in venues makes them the obvious choice.
Traktor controllers are nice and the software is cool for more creative mixing, but I very rarely see club DJs use Traktor these days which makes me worry about its future a bit. Also, if you use Traktor and ever want to play a club/venue, you either need to bring all your kit and your laptop, or you need to find a way to export your library to Pioneer format (I’m not sure if this is even possible) and then use some unfamiliar kit.
Denon gear is meant to be quite good, but again, your library isn’t in Rekordbox format which I think is a big deal. Serato seems popular in the hip hop etc. world, I’ve never used it so can’t comment, but I think it’s more aimed at people using control vinyl on turntables.
Most (all?) controllers just output MIDI, so you can technically use most controllers with most software (there are some quite nice 3rd party DJ apps without their own controllers such as Djay Pro), so you aren’t necessarily locked in to one software forever, but it makes sense to get the controller which matches your software of choice as it is going to have the best integration. Also, you have to pay a subscription (I think?) to use Rekordbox in DJ mode unless you have a Pioneer controller.