"quite useless" is a pretty strong adjective.
I've been using trickle chargers for nigh on twenty years after I used to suffer from going out on cold days and having hard or no starting, and the trickle chargers put an end to that.
The only negative I would offer about them, is they mask a degraded battery, such that the bike will start right up, then go somewhere thinking all is well, park the bike, return after work to find the bike will not start, until jump assist.
I have several bikes and backup generator on trickle charges, and all start, every time.