Answers

There are a lot of companies out there that will try and spin why certain cover products are better than others.  No cover product out there is 100% maintanence free.  And depending on how your roof line is designed a cover may not work at all.  I.E. Cut up/ short gutter runs and inside corners.

Any cover that messes with the last layer of shingles stay far far away from. Lifting the first layer of shingles can only potential do more harm to your roof than good.

 My professional opinion, install some sort of metal screen that locks into the lip of your gutter and clean them annually or bi-annually depending where you live and if your surrounded by mature trees.  Installing screens will eliminate the amount of cleaning done per year.