I also have one of these window perches - and my cats love it!! I have had several over the last 18 years, and they are always a huge hit.

I have painted wood sills, and in my experience the velcro strip always eventually separates from the sill (and yes, unfortunately, it does make quite a mess). What I did with this latest one (after it fell out of the window) was to use a carpet staple gun to re-secure the velcro strip to the sill. It seems to be working great so far - and I have seen ~24 lbs. of cat on it at the same time

PS. I don't know who was in it when it fell, but nobody got hurt, and they all started using the perch again as soon as it was back in the window.

Diane