staying put

I often 'complain' that 'my' Peregrines are masters at doing nothing, staying in the same spot for hours seemingly doing nothing, except for a spot of preening or paint (as a case in point, I spotted them on the same perches all afternoon today, from 14:30 until now), but they are real light weight compared to these 3:





I wonder how long these have been there, as I haven't been able to find anything about them, and how long they'll work.
Searching for them, I notice they cost around £25, and for a microsecond I fancied getting one to get rid of my pigeon problem...