Many engineered floors cannot no be sanded at all whilst others once or twice.
As far as the 25 year guarantee on the surface coating, I would like to read the fine details of that warranty. I reckon the floor would need recoating long before that. Its like the '50 year' and '25 year' gurantees given to different grades of treated pine - you would be hard pressed to find anyone who has successfully claimed against such a warranty.
Minx, the secret-nailer is a fairly standard tool for installing flooring. They actually fire a staple rather than a nail. Whilst they are a brilliant piece of equipment, I can say from experience your back feels it after three days use when not used to it.
Just read the warranty, it does not cover 'scrathes or reduction in gloss'
I guess, in the end, both engineered floorboards and solid timber should look the same. After all, up to 4 mm deep they are identical.