I bought a set of Tonica's a few years back just to try out and I wasn't really that impressed. I kinda felt like they were slightly similar to Dominants but not as powerful or responsive. However, even with that being said they do have a brighter sound than Dominant strings which does compliment certain violins.
My biggest problem with them was that after four weeks of gigging with them I had managed to break both my A and D string. At first I thought it might be a tuner issue but I realized that both had broken about 2 inches from the bridge itself. I guess if I were a rough player I wouldn't think much of it but before that I had never broken a string even once...well besides the E...everyone breaks those dang things every now and then.
You're right about them not outlasting Helicores but they are definitely a step up sound-wise.
Years?? I wish I got that out of my strings. The longest I've been able to hold off putting new strings on a fiddle was around 10 months. I have some classical friends that change their strings like clockwork every 4-6 months.
No, the expensive ones tend to be less strident or edgy. I guess it depends on the fiddle though.
I had a hell of a time finally finding a fiddle I could tolerate. For whatever reason, my ears would take any edginess and multiply it. Took me a few years to find something.
I noticed something was wrong when I was practicing with a rental fiddle, and wanted to smash it against the wall. It wasn't a bad fiddle, but my ear was not liking it, but I didn't know why. I just wanted to smash the thing. Luckily I figured out what was going on.