I have NOT used the Cobalt SS, but have more than 2 dozen of DCC Concepts Cobalt iP Digital under table switch motors (very similar to a Tortoise) on my layout, and have found them to be quite reliable. All have been operational for more than 3 years, and more than half for as much as 6 years. In that time, I have had only two issues; I fried the decoder on one during installation (lying on my back under the table, I should have double checked the terminals!). My fault, so I just ate the cost of a new one; the second problem, one out of a 12 pack arrived DOA. When I e-mailed DCC concepts, they had a new one to me in about a weeks time (pretty good, given they are in the UK and I am in the US). So, as a company, I can recommend them. My only caveats:
Some (not all!) of my iP Digitals are rather noisy (picture a nest of angry hornets). I have wondered whether a good clean and regrease would quiet them down... but I am loathe to do this without having a spare on hand.
It's hard to find a US supplier. My LHS carried them at one point... but the LHS moved (from a 5' drive to a 30 min drive), and the last time I checked, they had really reduced the breadth of inventory they carried, and didn't have the iP Digitals. I ended up buying the last couple off eBay.
I'd give the Cobalt SS a try... Good luck!