Air integration is somewhat difficult to manage, if you are going to rent regulators, because they have to install your transmitter or your HP hose on their regs. You don't need it -- it's perfectly reasonable simply to check your gauge at regular intervals.
When I said "constraints", I meant that you don't dive very much or very often and make your trips primarily for another purpose. In the grand scheme of what your travel costs, I'm sure the rental fees for a BC and regulator are not going to be a major issue. (It's different if you are doing a ten day dive trip and have to pay rental every day!) You don't want to carry very much, either. So it all adds up to renting the heavy and bulky stuff, and owning what has to fit (or, in the case of a computer, what you really need to know how to use, and want to keep for your own records).
When I said "constraints", I meant that you don't dive very much or very often and make your trips primarily for another purpose. In the grand scheme of what your travel costs, I'm sure the rental fees for a BC and regulator are not going to be a major issue. (It's different if you are doing a ten day dive trip and have to pay rental every day!) You don't want to carry very much, either. So it all adds up to renting the heavy and bulky stuff, and owning what has to fit (or, in the case of a computer, what you really need to know how to use, and want to keep for your own records).