I have one and it's fine. I've not had a cake slide yet. Although, I've read where some people have. Honestly, though. While it makes things a hint easier, it's not enough of a difference to justify the price. Spend your money on some other can't-live-without toy.
I have a total of three turntables.
As for the higher turntables, I sit mine on an inverted cake pan without any problems. You can do this and not need to tilt your cake.
Rectangular base? I place a large inverted cookie sheet over my turntable.
If you are having issues with sliding due to the makeshift turntables I have suggested, purchase some non-skid shelf liner. Nothing slides around on that stuff!
I save money where I can so I can spend money on the truly hard to live without items.