I have built quite a few rails apps using TR. The braintree ruby gem makes the whole process very easy. I would hesitate in using this because you still end up explaining a lot to during PCI compliance. IIRC during the PCI compliance my customers had to do a whole lot of work even when we were using TR. Splitting your process into multiple steps and doing validation using JS is much much easier IMHO.
The compliance process varies depending on how the business operates. There are more controls if you accept card numbers over the phone, for example. For most merchants, the process is straightforward. Our PCI Compliance page describes the process using Braintree.js.
