The climb is a bit demanding for bad knees not just because it’s high but also the a bit rough and narrow stairs. The view really worths the climb. The deck is also a bit narrow.
We went to Tallinn in May and the town hall tower and many other towers were closed in May (actually many of them are open in Jun-August only) so this is the only tower we could visit. Can’t do any comparison but I guess the view of town hall tower is also nice.