Mostly that explained it best I suppose ^
Unless there's a limit put where you'd allow only 1 or 2 pokes to be rented at one time, it'd be better. I don't see why people wouldn't just abuse this if no limit, and get 6 pokes out of this and have a team temporary. Yeah, they'd have a shit randomly built team, but it's still abusable, and gets you saved last minute or something.
Also, I couldn't help but note this...
I hope you mean manually change movesets and evs, because if not, that's totally contradictory.
Even if manually, and I know you said 6 hours just for example, but that'd be not a lot of time to change much, so I suppose most wouldn't even bother to it, seeing as how it goes away after it's returned anyway.
It'd also balance people not abusing this too much, and eventually build a comp for themselves.
If I'd say, I'd use this only if I want to test new shit or just randomly want to try and see what pokes I can find, because I'm a curious fucker like that. That, or if I'm in a pinch before a tour or something, which I doubt, but it'd def help out newer players more.
All in all, I suppose I like it, wouldn't be bad to have it mostly like this