What is this gun magnet for ?
The dimmension: 4.1*1.5*0.3 inch, compact and low-profile, designed to conceal & stock mags, handgun, shotgun & rifles, not for quickdraw.

How many pistols or mags can be held with a singe magnet ?
2 pisols, 1 pistol with a spare mag, or 2-4 magazines of pistol(steel mag, not aluminum or polymer)

Can I stick it to safe door directly without adhesive tape or screws ?
No. The back side is not magnetic. You need at least the tape, or if possible, use the screws together.
Do clean the surface to be mount carefully, press the tape with effort for 10s, wait 36 hours to ensure adhesive fully bound before stick your guns on.

My car is new and I prefer not to drill. What is the solution ?
Although VHB series tapes are highest class of 3M, they do not guarantee no any fails due to heating, aging or mis-operation. Especially, vehicles may hit bumps during off-road driving or in case of emergency,
it is strongly recommended to use tapes & screws together. In fact, only 2 tiny holes and can be easily filled in glues or other filler in same color.

Will a single magnet holds a long gun vertically with the butt resting on floor ? By the receiver or barrel ?
Whatever a receiver made of polymer or aluminum, the barrel is carbon steel. So get the barrel contact as much area as possible and adjust angle of rifles to suit the spacing created by hand guard

Is it hard to release since it is so strong ?
Pulling against the magnets is quite difficult. Slide you gun along the rubber and it would not take much effort.

Does the magnet gun holder work with polymer or aluminum ?
No, they are not magnetic at all.

How many I need to mount a rifle or shotgun horizontally for display ?
2. One for barrel and the other for slide or receiver which is steel (magnetic). Get as much contact area as possible.