My spinner is square and I inherited it from someone who didn't want it anymore. I use it more with my students than I do myself.
I position my student's foot with the ball on the center of the plate, then have them hold the free toe behind on the ground. I don't have him/her push with the free foot, they use the upper body to start the spin, then bring the free leg around from behind to the front to hold in an open position. It's tricky, but they have to learn how to square their hips anyway, so it works. Arms check to center in a rounded position to continue the spin.
Once they get 3-4 revolutions in the open position, I then work on the four positions of scratch spin, adding one position at a time. They only get 1-2 revs/position, so it's really rushed, but it works okay. The trickiest part is to check arms and legs at the same time.
So, please, no comments on how the money's better put into ice time.
But what you've described is exactly why a spinner is not a good purchase for skaters who don't know how to use it and aren't taking off-ice classes with someone who does. This is a perfect example, even though it's not your money that was spent to buy the tool.
Doesn't your coach know how to use the spinner? It's hers, right? Seems a little zany to give it to a student without any instruction or guidance. I only let my students work with it off-ice under my supervision and I spot them to be sure they don't fall hard. Several have flown off the spinner when they lost their balance. On a rubber floor, it's very easy to sprain an ankle or take a tumble since you stop abruptly.
Using a spinner only makes sense where there's no appropriate flooring, like the back of the ice rink that has rubber floors, or a carpeted party room. Otherwise, the spinner is just an expense that can easily be eliminated by using socks and a smooth floor in an open area.
As for your improved backspins, sorry, but I can get the same results on my kitchen floor, lol. I get twice as many revolutions on the spinner, but that's because I took an off-ice class on how to use the tool and I know how to control and balance on it properly.
A few months ago, SillyAdultSkater posted this tip for using a spinner for turns. I loved that tip and used it to master the FI3/crossover/mohawk/repeat end pattern for synchro.
http://skatingforums.com/index.php?topic=504.msg3966#msg3966I also use it to teach the hip close snap for backspins. Similar start with the free leg behind, turn to close the hip and pick up the free foot in front. It's just as easy to do without a spinner, but not as much fun.