Buy whatever you can find cheapest from China, they are mostly the same card.
About the usefulness, yes and no. If it's a clear fault at one of the POST stages (i.e. memory fault) then it's possible to narrow down the problem. However, if the problem is the mainboard itself, things get more complicated as the POST might hang at different stages and give you different error code each time. Then it becomes somewhat difficult to determine where the problem lies. Tt could be the voltage, voltage regulator, tantalum caps etc. and therefore you need to start hunting the actual cause with a multimeter.