With ebay and cheap pen lasers it really comes down to luck more than anything. You'll probably get at least 10mW of visible 532nm, most likely around 30mW. Anything beyond that consider yourself lucky.
I've also had mixed luck with the non pen models, a few companies sent me samples about a year back, even though I told them I probably wouldn't have time to review them... as it turns out I didn't, but I did get around to lpming them. Despite them being advertised as 50mW, 100mW and 150mW, the best one hot only 75mW and wasn't very stable, one barely put out 20mW, and the "50mW" version was just ridiculously unstable, jumping from ~10mW to 40mW or so.
I know it's not what you want to hear, but you're better off buying from a known company, and paying for a specific power. O-like pens do actually tend to live up to their advertisement in my experience. The 50mW non pen lasers, with glued crystal would be my choice on a budget, of course you'll still end up spending way more than the $5-$15 you'd need to spend on ebay.
