A problem with bank "mileage" programs is that they limit you to award tickets that would be cheap anyhow. Where it says "subject to space and fare availability" it means that if a flight doesn't have a really cheap seat open, you don't get it as an award. So, while it is technically true that the program has no blackout dates, airline capacity controls on deep-discount fares create the same effect in practice.

The highest-value awards are for travel without a Saturday night stay, last-minute travel, overseas upgrades, and things like that. You can't get those with this sort of program - the bank buys tickets with real money, and these cost too much.

Another downside is that you can't combine miles in such a program with miles from any other source. Unless you plan to put your company's office supplies bill on your card or you're building a new home with lumber from Home Depot, it takes forever to earn an award. Balanes build up much faster if your flights and hotel stays count too.

That said, there are people whose needs and travel patterns match these programs well. Just make sure you're one of them before you sign up.