I guess it kinda depends on how you feel about your car. Other coolants wont destroy your engine (maybe not while you own it at least), but sometimes there's the stuff that's "supposed" to go in it.
If you find a decent deal, a gallon of BMW coolant is about $17-19. Then mix it 50/50 and you have 2 gallons. That's enough for most cars. For something you only flush once every 2-3 yrs, a few more bucks for a little more peace of mind seems worth it... just knowing it's right. If it were a beater car, I wouldn't care, but most euro cars, I try to stick w/ the proper brand coolant... if at least to keep the proper color coolant in the tank
(BMW= blue, VW/Audi= pink or purple, but a Honda... regular green stuff is fine.)