Condos, cash flow & 50% rule

[Bienes Raices]

I've read a lot of negative things about buying condos for rental. But even though you would pay somewhere between $200-$400 in monthly maintenance fees for the unit, isn't that offset somewhat by the fact that you won't be paying for big ticket repairs in the future, like a new roof (or if you do, it's spread across all the condo owners as a special assessment)? As well as the fact that you never need to do any exterior maintance, or dealing with tree, fence and driveway problems?

So, for example, I buy a condo for $25K that has a $300 monthly fee, and will rent out for $700/month.
I subtract off the $300 and pretend the rent is $400/mo. for argument's sake. Do I still need to apply the 50% rule to that $400/mo., or is it more like the 20% rule now? From what I can see, the only costs would be insurance, property taxes, possible eviction, and minor repairs to plumbing, new carpet every couple of years, painting.