Very mixed feelings on this do to a bad experience. I would normally say Ok as long as there is a witness in the "you brake it you fix it & cover any insurance increase costs that might occur" before the swap.
I had the opportunity to try many different bikes this year, mostly other bikers were asking to try the Triumph, so they asked me. It was sweet to see how my bike looked and sounded on the road and to try others in a real world test.
One lad I "used to" ride with, has a Busa & was letting several try his bike so I asked him for a swap. This guy normally putts around in 6th gear all day pissing everyone off by riding too slow. Anyway, he jumps on my bike & smokes away. Riding at very high speeds & taking risks. There is a nasty set of railway tracks that we would normally go very slow over, not buddy on my bike. He hit them fast & hard. I'm not used to his bike so I take it relatively easy but can keep him in my sights. He finally pulls over & the first thing he says is "Wow this thing flies, I kept smashing it off the vev limiter" and starts laughing. I wanted to punch his face off, kick his groin, gouge his eyes out, I was so pissed off. I thought for sure this would be a good guy to let ride my bike, boy I was WRONG. I don't even ride with him anymore and wouldn't let anyone ride my bike again.