There's also an extent to which while learning an instrument you try to sound like everyone else. But when you drop a clanger, it's very much your own clanger.
I wouldn't expect that a group like the Portsmouth Sinfonia or the RTO would shed great light upon the music they were playing, but I can imagine it being an interesting experience. More to the point, an experience whose interestingness (and entertainingness) would depend very directly on the performing qualities of the musicians - in a way more so than in a 'normal' orchestral concert.
I've done vaguely similar things, attempting to perform on colleagues' instruments for more or less extended periods - never a whole concert though and if I happened to get a call from the RTO and could spare the time and they wanted me for an instrument I was curious to muck around with I'd certainly be up for it.