Practically, Runbox gives you much more aliases. You can use their own set of domains for each alias which is not small. Can't tell exact number now but around 30 or so. Really handy. There is another problem though. After you've done with many aliases and domains it's getting more and more difficult to maintain. You have to at least vaguely remember which one you have used already. I wish they could introduce a better way of managing aliases.

Is there any technical reason for charging per alias? It’s just an extra $0.00000001 database entry per, no?

It might be to slow alias namespace depletion, and put a cost on potential squatting.

Makes sense on their domain, but if I’m pointing my $1.95/year .info domain at them, I don’t understand the limits.