I bought these to make my very different looking humbuckers look more uniform, and fill up more space in the pickup cavities since my dimarzios are a bit small for them.
Personally I didn't notice change in tone, EXCEPT for having to lower the pickups if the covers are getting in the way of the strings. Unfortunatelly I couldn't get my neck pickup to fit in perfectly inside the cover, so there was empty space between the top of the pickup and the the cover, which resulted in the cover touching the strings at times. Option was to lower the pickup, but it needed to be too low, which resulted in thin tone. Other option would be to try file the pickup but I didn't want to ruin the it. Bridge pickup fit in fine.
All in all, simple and cheap upgrade, but might require some alterations to pickups themselves to fit perfectly.