Using strong magnets for hanging window blinds
You need to worry about not just the weight of the blinds, but also a weight slightly greater than the blinds focused at the string when the blinds are pulled up.  I'm going to make up some numbers, but if you had a blind that was 10lbs, you would see maybe 7lbs on the left bracket and probably upwards of 20lbs on the right bracket (assuming string on the right) when they are lifted.  The weight of the blinds plus friction is going to add up.

I have some 6' blinds and haven't measured it, but it takes a lot of force to raise them.   I normally lift them with my free hand as I pull the string, but my wife isn't that "nice".  There's also some lateral force if you're not pulling straight down and when you have to pull sideways to unlatch the mechanism.

Any pull force listed on the magnet is in a purely perpendicular force performed in a lab.  They are very, very strong, but I wouldn't trust a "working load" with that listed weight.  You're going to get a stronger hold from a mechanical fastener like a screw or bolt.