I just bought one from RH Tubs and its a nice cover. Its a 6" to 4" taper and got it with double wrapped cores. I highly recommend the cover. The 6 to 4 is their extreme cover and the double wrapped cores were an up charge of $20. The cover is 92" x92" and it cost under $400.
I printed out the order sheet, did the preliminary stuff on there then called it in, wanted handles in certain places and they sent me a CAD drawing to OK ... I had it in 4 weeks. I don't know what a factory cover from Thermospa is like but it is much nicer then my factory cover.
If you have any questions let me know.