The Japanese actually had a very similar, although better, design called the Sen Taka. They didn't get any into the water until the war was effectively over and none made a patrol.
The boat, especially with the Type 95 torpedo, could have been a roral pain (assuming the IJN actually figured out how to use subs, which wasn't too likely).
http://www.combinedfleet.com/type_sts.htm
Given the propensity of high test H2O2 to go boom when just looked at funny, I don't think I'd enjoy the survival chances of one under depth charge attack.....