Angie's List is offering a "Big Deal" of up to 50' of gutter cleaning and installation of protective covers for $299. Supposedly a $498 value. This is on LI, NY.

Does this sound like a good deal?

If it is a good quality gutter cover (such as Gutter Helmet), it would be a great deal. But- there are many types of gutter covers and I have tried them all. The only type that worked for me was the type that works by surface tension, like Gutter Helmet (see link below). Some screens are just plastic grids which clog up worse than with no cover, especially if there are maple trees around. But my former home where I tried the screen type (which didn't work for me) was surrounded by tall Poplar trees. Depends on your conditions. I obtained an estimate of $ 10 per foot from a Gutter Helmet dealer more than 10 years ago so if it is Gutter Helmet they are proposing, sounds like a great deal. But my hunch is that it is one of the plastic screens.
For example, I just saw a price of $ 44 for a package of 25 of the plastic covers (3 feet long each I think but it didn't say). For 50 feet of gutter, they would need 17 of those which would be about $ 10 worth, and they just snap into place so about one hour labor at most, and they could clean the gutter as they installed the new covers.
The key point for you is to find out what type covers they are proposing I believe. Good luck.

This is the Gutter Helmet concept: Find Out How Our Gutter Protection System Works Here | Gutter Helmet

$6 per foot seem high to me.