I have a couple of wonder bits - they're lovely. I've had them both for about 10 years and they suit most of my working horses. They are western bits and have been around for quite a long time. One of mine has a french-link lozenge and my other has a chain. The chain one is generally preferred by my guys. They work calmly in them and I have always been pleased with how the horses go - nicely forward going but if you need to stop in a rush then you can...having said that my working guys pretty much stop on a dime anyway regardless of which bit they have in their mouths.
I can't really tell you what sort of action it has as I am a western rider so we don't have the same contact as English riders. I would guess that a sensitive contact would be advisable, although with the one you are looking at I doubt it is much different from the action of a Dutch gag.
What your horse may like though, is the fact that it is sweetiron. I tend to only use sweetiron bits or KK Aurigan bits on my young horses as they love the flavour of them. You should find that your horse will salivate more and be more accepting of this bit.
I am very impressed at how cheap that bit is on that website though - they are much more expensive over here.
I have a sweet iron copper tom thumb - about 4 bits down - and it has a 'rough' side and a 'smooth' side so you can put it two different ways round in the horses mouth
the rollers in the middle help the horse to mouth and soften and I find it great for horses that are normally 'nice' and have good mouths but just need a little bit extra for jumping
all the horses I've had that bit on have gone really well