Well, first of all I'd like to quote Dopaminer on the SpinFits...
That being said, personally I think rotating tips are a bit of a gimmick - why would we need them to rotate anyway?
On the other hand, the ability to curve and adapt to the shape of your ear canal seems more useful, but in my experience it comes at a price. Like I said, the silicone used is very thin (similar to the Philips SHE3590 tips). On the plus side, that makes the tips very comfortable and easier to fit deeply. However, it also offers less support than regular tips and is prone to warping, which may result in tiny leaks. Hence you may end up with a deeper seal and more bass, or a leaky seal and less bass, depending on the shape of your ear canals and nature of your fit.
Another reason for concern is that the SpinFits' opening is narrower than the JVC's nozzle opening, and due to their soft / flexible nature they may become even narrower as they adapt to your ear canal. This creates a (slight) reverse-horn, which may reduce treble extension and make them sound bassier and somewhat congested, depending on the severity of the effect.
Most of the above is pretty individual though, so what works for you may not work for someone else and vice versa.
Last not least, the front-mod should work well for those who're getting a secure seal with SpinFits, but others with an already leaky seal may find little or no difference after the mod.
I'd say they operate in the same way the GR07 nozzles, they allow for that perfect fit
I do hear a bassier sound with a lot of earphones, so maybe I am getting that reverse horn effect. I don't mind it actually since I dig a warm sound on public transport
It's weird how the Ortofon tips are so popular yet they have a similar opening diameter and silicone firmness... I actually think of the SpinFits as a bassier Ortofon with insane comfort