I have not heard anything definitive re the same power or not, although anecdotally they seem close.
People primarily choose OMS over Jets when they are foot heavy and have issues keeping their legs in proper trim, since they are not as heavy. I would guess a mojority of people benefit from the weight, and list that as a positive for the Jets, but for those that don't, the OMS fins are a great option. Weight issues aside, they are nearly identically shaped so they kick pretty much the same as regular Jets, as far as alternate kicks and such.
They cost more, naturally, so I'd stick with Jets unless you need the weight characteristics of the OMS fins.
As for spring straps, I don't care for the tube-style straps (they're not comfortable to me), and prefer more of a heel cup (esp. one with a good pull loop), so I use these reasonably priced straps with my Jets:
http://www.divesports.com/mall/innovative_acc_springstrapsjetfins.asp