put it simply the guide number is different... FL-50 = GN 50, FL-36 = GN 36.
What GN means in lay man terms = maximum distance it can reach with ISO 100.
In terms of size... the FL-36 is about 2/3 the size of the FL-50...
for home use and portait... i think the FL-36 is sufficient. The only problem is the recharge time of the flash. Thats also because it uses 2 AA batteries instead of 4... which makes is lighter also.
For Super high celling like a convention hall... ya.. u'll need a FL-50 to bounce... which might not be enough also