I have no idea what the brand is but we've had our black out roller shades in our bedroom for close to 20 years and they are up and down every single day. I bought them at a local independent hardware store - not sure if those even exist anymore! Never had a problem with the springs and the edges aren't even frayed. We did the opposite of your set up. Ours are inside mount and I have a roman shade that is outside nmount, that 'hides the blackout shade. No light leak to speak of. If I had to buy them again, I'd contact an independent drapery house and ask what they use. They do more than the pretty curtains and have to offer a quality product. It will probably cost more than a department store but if they work trouble fee it may be worth it.

Hard to say as this could be a room-by-room decision, depending on what would look best in each location. I'm thinking white might look quite sterile. Any chance of some pictures o the rooms concerned?

That is really just a personal preference. I like light in the morning so I usually have no shades down in the bedroom, but I did install some blackout shades because my husband has to sleep during the day sometimes. I thought that gave us both options

Hunter Douglas definitely has 50% darkening. We have total blackout duette by HD in the front of our apartment which is street facing and also several SUPER bright street lights and floods. In our 3rd bedroom which faces the interior “donut” of our block, we have HD duette which are probably 50%. The seem like what you’d describe. You could also do something else: light filtering roller shade with a Roman blind on top. That way you’d get customizable privacy and light blocking depending on the time of day and your needs. The Roman shade could even be blackout.