My RC friends who use LiFePO4 swear by them. They handle high amperage drain and can be charged at higher amperage than other battery technology. They are not as popular in RC as they are heavier and larger than equal LiPo amperage. These differences are not a concern for sailplane use.

And of most importance, LiFePO4 cells do not have the explosion/fire risk of LiPo cells if charged incorrectly. FWIW,all LiPo cells I've seen are flat and thin and rectangular. All the LiFePO4 I've seen are cylindrical.

Absolutely, Lipo cells require balance maintenance. I cannot confirm but have read LiFePO4 cells are self balancing when connected in series and do not require an on board balance circuit or an external balancing plug.Please do your own due diligence.

Other than K2, all the LiFePO4 packs I've seen were home made packs using cylindrical cells taken from DeWalt tool power packs. It is my understanding the DeWalt cells are actually A123 brand LiFePO4 cells.

This is an outstanding battery and charger forum. http://www.rcgroups.com/batteries-and-chargers-129/

Safe flights.