First regs I bought were used SP Mk20 ultralight with a G250 and an Air2. They had the unused rebuld parts in a baggie with the recipt for the rebuild attached to the reg. (true someone could have staped it there after the fact, but i believe they had not been used since the rebuild.) everything worked great for 3 dives. Dive 4, the air2 started leaking. I brought it to the shop that did the service, along with the documentation. They charged me full price for another rebuild, basically this told me they didnt stand behind their workmanship. Say what you will, this left a sour taste in my mouth.
Second regs I bought: brand new Legend LX ACD with matching octo. They breathe harder than they SPs and I found myself constantly spitting out more seawater than I had noticed before, but they dont leak air and they let me breathe under water.
Then a very good friend turned me on to HOG. The user serviceable portion of it got me interested, but meeting chris at the scuba show in long beach sent it home for me. Now I dive a set of DIN HOG regs with a long hose setup, and I can't think of a single reason I would ever leave it. (unless I left it for 2 DIN HOG regs on a set of doubles)
The SP is being delegated for a sling bottle, and the Legends are waiting patiently in the corner for someone that wants them. I don't have the heart to give them away, but I would have a hard time with my self if I tried to sell them for more than a set of new HOGs to try and get my investment back.
Just my $0.02
I am not a Pro. I am a pretty new recreational diver. I just happen to have have a new divers perspective on a few regs.