I think what I've landed on, more or less is that if it goes INSIDE the engine, I won't muck around. If it's on the OUTSIDE, then it's worth investigating other sources. In this case I class the oil filter as INSIDE because it effects the oil which is 'inside'.
So, while no one was able to tell me if that dealer was reputable or not, I went and bought it elsewhere. You had to contact them first to order. This is the 21st century. Click n pay, baby!