Its gonna be difficult to pop balloons with 50mws of green. And the focusable laser you posted can only focus outwards; to make the dot bigger, so its not really designed for burning.
Re: Review of Rayfoss 200mW Green Focusable Laser Torch(RF 532-200mW-FLX)
O that is more than enough heatsinking, it just needs a duty cylce cause its a low quality module!
%50 efficiency doesnt seem right... I think the highest ive heard of is %30...
That being said the only way to truly find out your lasers power is measuring it.