i do not ski park - yet - so i might not be the best to answer any park related question. The reason i mentioned the more centrish mount is that the sweet spot position is a bit set back probably to accomodate better on piste/soft snow skiing. I just assumed that if buttering and railing was the main goal - and not soft snow performance - a more centered mount might be better,
the skis are not terribly stiff - yet no noodle underfoot where they are pretty supportive. The tips and tails are pretty soft though, so yeah, i think they will butter with ease. I do not think that Lib's edges are any more prone to cracking than any other edges, with or without mini mag.
Of the two i preferred the ufo100 over the ufo115 - the latter was just too soft for where i i ride and the kind of riding i do. I suspect that a lot of jibbier freestylers will quite like ufo115s, especially as soft snow playstick. For me, transitioning between icy groomers and tracked out soft snow, they just did not behave as i wanted them to. I bought them mainly to try them and to gain experience on that kind of a ski, so i am glad that i tried em. If i lived in a spot with more flyffy light snow, i would probably have retained them. The ufo100s did work well for me though, but decided to try something else in that segment as well - something a bit more symmetrical and narrower up front - instead of remounting them. I am not sure if that was the best decision, but alas, too late now
for the price they charge right now you get a lot of high quality ski for your money. The dimensions are pretty decent and not very controversial, the graphics are kinda nice as well, so i think they are def worth a go. They are very intuitive and easy to ski. If you for some reason do not like them, selling them on at a (for you) decent price shouldn't be too hard, especially for more recreational non jibby skier that the ski works very well for in the sweet spot mount.