Don't know if this is helpful or not, but... got mine from Sdumper as well. It has a 3/4HP pump and a large (approx 1ft by 1ft COPELAND condenser). Without load it'll bump up to -53.5C , under load it's never gone above -40C, and that's after some serious benching. Has an evap tube about the size of an elephant's trunk, so positioning is no problem, not like those overly expensive Vapo-Chills.
Refrigerant I believe is R507, but like supes says, some of the custom builders add some exotic blends that give them better temps.
The unit came with a temp probe embedded with the evap tubes and plugs into any type K thermo - You can get a good one from Extech for about $100 bucks. If you're into tweaking you really need a true RMS DMM, and Extech has one of those for about $140 that inlcudes an IR remote temp gauge.
What you can do with your rig makes water look a lot like air. It's a whole new ballgame with an ss unit. Have admit though, I'm starting to long for a cascade, or, maybe winning those LN2 pots lol
and yeah.. people who take a down payment tend to take a lot longer to build your unit. I didn't pay a cent until the unit was ready to ship