Thanks for your question about air vests! Air vests are a hot topic among eventers and I am a big supporter!! There are two major brands: Hit Air and Point Two. Both brands are incredibly reputable and provide equal safety, in my opinion.
There are different models of air vests, some of them are “hybrid” (Tipperary, Charles Owen etc) which combine a standard type hard shell vest and the air vest. The original is just the air vest, which should be worn over a standard hard shell vest.
I tend to find that the hybrid feels more bulky, where I hardly notice wearing the original air vest over my Tipperary. I would recommend to try both versions, and also be sure that you have the correct size and fit once you find the version that you are most comfortable in.
Lastly, all new things take getting used to, be sure you wear the new vest around and jump in it a few times before you go cross-country. I assure you that the safety that the air vest provides will quickly over-rule the original discomfort!
Good luck, and happy eventing!!