I also had the Spencer mod done to my 09 seat. When I first got it back, I posted a raving review on the old forum after about 300 miles riding. Now I'm afraid that I'll have to change my tune. Let me say first that the service was quick and very inexpensive. The mods performed were EXACTLY what I asked for, it just turns out they were not what I really needed. My long range observations include: Supracore is not for me. At 275 lbs dry, I think I just crushed the life out of it. I seemed to be sitting on the seat pan. My request that he take the pressure off of my thighs at the edge of the seat was ill-advised. Turns out, the pressure was moved to the middle, just behind the jewels, to an area called the "perineum". (don't look it up, it's not pretty). Anyway, the result was nerve damage, and my urologist gave me an ultimatum: Get a different seat, or give up either riding or sex, my choice. AAAARRRGGGGHHHHHHHH!!! Talk about a tough spot to be in.
Don't get me wrong, so let me reiterate: Spencers gave me what I requested, quickly, and for a low price. I just did not ask for the right things.
Anyway, I ended up getting the seat re-done by another outfit, called "Mean City Cycles". This time around I had a much more educated list of requirements, and spent quite a lot more money. Quality and fit are just right for me, and I've put a few thousand miles on it so far with great results. Service was adequate, can't go any higher than that, unfortunately. What prevented a higher rating? They had an equipment failure that caused them to miss my appointment window. Okay, stuff happens. But when I requested that they upgrade my return shipping so I could have the seat back for an important date, they said "sure, but you pay the increased shipping." It was only $29, and I am sure I won't die broke because of it, but it wasn't my issue that caused the delay, and I just don't think I should have had to pay to make it right. But they had my seat, so what could I do? I'd still recommend their product, and I've seen their service after-the-sale, and it was impressive.
So, if you know what you need, I'd say you can't go wrong with either company. Just didn't work out well for me.