Hi Norbert,
it's almost the same size, than the 2S 1250mAh Lipo. Also the weight doesn't differ: Both battery packs weigh about 95g including cables and plugs.
I've got a similar pair of Li-Ion with even 3000mAh for testing but they only allow a discharge power of 10A so they will likekly be too weak for a copter but at least good enough for transmitters.