I don't know about those triggers; I make my own and they work just as well as centred ones - the only con is that you don't have positional sensing.
Here's a picture of one of mine:
I put a couple of strips of foam underneath and a small circle on top. Note how the piezo has lots of space to flex. The bracket is made with a piece of plastic but you can use any L-bracket.
Here's a pic of a dual zone trigger with a pot for the head piezo:
And a video of how it triggers: