AW has been selling them in his sales thread for quite a while. They work well.
That should be quite a nice set-up. You are right that you will need the soft-start. You should get nearly 20 mins run-time, but limit it to 15 mins to avoid over-discharging the cells.Do you think three of them would be alright for a Mag85 in a 3C body and AW soft start switch?