minoxidil is minoxidil is minoxidil....well just about.
The stuff at Walgreens will be just as good as Rogaine/Regaine and will deliver the same results.
The only really different minoxidil is Dr Lees 'Standard minoxidil' this stuff dries in 10 minutes (Rogaine can take 2-4 hours !!) and is not greasy like Rogaine, I personally, cannot go back to Rogaine or a generic after trying Dr Lees stuff, it is very very good.