Does it allow for multiple sheet to come off or will the arm always force the towel to rip at the next perforated part?

It will allow for multiple sheets to come off.

Does the base use suction to stay in place?

No not suction but it uses a grippy felt material. It's a solid product and doesn't move easily

Would anyone kindly provide video of this paper towel holder in use... successfully tearing a single sheet off one-handed, as advertised? THANK YOU!!

No video but can confirm it works as advertised

Is there a way to fix the spring on the arm after it breaks?

I fixed it with a rubber band and twist tie. If you look at the underside of the holder, there are 2 slots where you can see a little lever in each slot. When you move the arm, the levers move. When the arm is held close to the center post, the levers move close to the openings. When the arm is extended away from the center post, the levers recede into the base. 1) With the arm held close to the center post, hook a rubber band underneath each lever 2) Stretch the rubber band so it hooks onto the arm where piece that rests against the roll of paper towel meets 3) Use a twist tie to secure the rubber band so it doesn't slip off We'll see how long it lasts (until the rubber band breaks)...