Static contractions, including glute squeezes, are easy to do at your leisure, sitting, standing, even laying down, and are proven effective. Was how I kept a bit of strength while in full traction.
If you have the ability to do them in various positions do so, it helps build strength in various positions. They are safe, unless you have connective tissue damage, and difficult to overdo, not impossible. I would always advise doing these in short bursts frequently throughout the day. You will get funny looks, consider you are basically doing short pelvic thrusts timewarp style. I was single when last using some of them and when there was a smile was arrogant enough to use this as an ice-breaker a few times, in case you are wondering the young pelvic thruster who could hardly walk didn't fair too well 99% of the time, but had a good laugh trying.
Good all round, no, good yes. Static work is basically isometric in style and the major performance limit on isometric work is that almost only builds strength in that one position. This means you could do squeezes in your chair all day and it wouldn't be much help for you walking where you need to have strength in various positions through the movement. However one of the most important parts of remedial work is stopping muscle wastage, and this helps that immensely by activating them you tell the body this is needed and it will not regard it as potential energy. It also forces the body to repair it and this means nice consistent supply of nutrients and even some potential for growth, very, very little.