While I don’t really use Flip at all (as I usually play with Mixvibes Cross), I know you can use it on the SX, just not marked as flip as on the SX2.
Another thing is, whatever you buy, unless there is a really innovative thing you need/want, like Stems, it will support all functionality that the supported software has. Depending on the software you can often change mappings to suit your personal needs. After buying it will then have to last a few years (3-5 imho is a realistic outlook if you spend that kind of money). Again, unless something like Stems comes along (which isn’t for all or even most DJs!), chances are that you can continue using your controller through all the changes in the software.
Take the SX/SX2 differences, it’s mainly RGB instead of regular performance pads and the DVS option. Both are hardly game-changers and both would not be a reason for me to “upgrade” my SX to an SX2. Actually, if money was tight, I’d be just as happy getting a cheap but nice SX rather than a new SX2.
Either way, you’d just postpone the inevitable, your controller will become obsolete to some new functionality in the future. As development never stops, waiting for the next new controller will have you waiting forever.
Frankly, do the math (workflow, software, budget, CURRENTLY AVAILABLE controller), buy your final choice and get cooking.
Any more time spent on the whole gear debate is time not spent doing what will improve your skills far more than a few buttons or knobs: practicing and playing out!
The only exception I would make is when something is announced that you really like and not yet available. The current example being the Denon MCX-8000. If I wanted a new controller and that one tickles my fancy (which is does in a major way btw!), I’d be willing to wait a few months for it to come out.
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