I too own a Tipperary vest...it's all I could afford at the time as well, and a vest of some type is required to Event, at least in my area anyway!! I've fallen in mine a million times and it's always protected me.
Someone mentioned above that it doesn't protect against whiplash...but what vest does? You'd have to have something supporting your neck to avoid that and the vests, that I have seen anyway, don't have anything that would.
"The times when you have seen only one set of footprints in the sand, is when I carried you..."