yes, they are 80% interchangeable, unless it's some special bladder/wing or backplate design with odd-size mounting holes etc.
if you go to any shop with BP/wings on display, you can easily see how everything fits together and can be mixed and matched. best if they have several brands.
anyway most BP BCDs function more or less the same... it's just what brand it is. you might want to consider things like single bladder vs dual layer construction, location and number of dump valves, length of inflator hose etc. otherwise they will all do the same job, so budget shouldn't be a problem.
oxycheq setups are good value for money. but if you're feeling rich halcyon works too.
i know diver's outfitter just brought in some oxycheq stuff maybe you can go take a look. going to pick up my travel plate from them this weekend!