I have cordless blinds and rarely have had any issues and the issues I have had I was able to fix. I once read pull them straight out perpendicular to the window until you feel a pop and then it starts working normal again. I am not sure if that is what you meant by exercising the tension mechanism, but if not that has worked every time for me.

As for if it's the cordless blinds, I have $7 blinds from Menard's, so I am not talking expensive or nice by any means. I assume they are store brand, since they are 27x64 and only $7. 3 kids that kept destroying blinds for one reason or another, so I ended up going cheap and they are going 4 years strong.

Somewhat OT, I've never been impressed with HD brands. At best, they're clones of one of the popular models. Much more common is that they're a lower-quality version. Corded blinds are unlikely to even be available these days, as they are a safety risk.

Certainly do some research before buying. Googling for "[brand/model] complaints" or "[brand/model] problems" tends to be helpful. If it exists on Amazon/etc, sort reviews by date, and look at the most recent to avoid fake reviews.