Little Battery Tender and you're good to go, I think I got the Junior model and I think that's the one you must be looking at at Walmart for that price. Make sure all your connections are good and snug.
Same here, no problem. You want to hook up something cheap to your $20k bike.....that's your business. I've had the same $38 Battery Tender Plus for the last six years, on 3 bikes.
Same here - Battery Tender Plus for several years on quads, bikes and lawn tractors, still working great. And I go directly to the negative terminal.
The reason you go to the frame is to limit current and protect the electronics. The tender is safe as it has the controls right in the unit. Very little amps at any time.