I tried it for AoC 2024. I'd always been curious about it. I wouldn't call it overall easy to use. That's partially due to the way AoC's problems are structured (reading matrices and all that), but there were more general pain-points as well, and there's surprisingly little info about Ada online. Looking up something as simple as converting an integer to a character took me quite some time (also hindered by the seemingly random way Ada uses attributes; sometimes you use a type, sometimes a variable; sometimes it's a constant, sometimes a function, or a property). But it definitely has its positive aspects.
I tried Ada because of Spark, but unfortunately, that's to deep to get into just for a few puzzles, and has an even worse online presence.