I'm using the Jaya mains conditioners, Roraima and Roraima+ mains cables for CD player and amp, super Kinabalu for both CD player and amp, and mini-Moncayo speaker links. I also have a Silver Solfonn balanced interconnect .
I've borrowed bits and pieces from Jeremy from time to time and liked what it did.
The key is vibration cancellation; the cables themselves in the kit that I have are nothing special although they have since brought out the 'Silver' range which is supposed to be another step-up in both quality and price.
For me, it has the biggest impact where vibrational energy is greatest and that's at the speaker end of things. My speakers are bi-wirable and fitting the mini Moncayo speaker links made a huge difference over the stock bridging straps and DIY cable links that I'd been using. It was like listening to different speakers so I'd suggest that the links should be the first port of call for anyone wanting to dip their toe in the water, providing they have bi-wirable speaker terminals. Jeremy demonstrated the Moncayo speaker cable against my old Chord Odyssey and again the differences were not subtle although they shouldn't be if you consider the difference in price. That will probably be my next upgrade.
The super Kinabalu under the CD player also works very well where it just seemed to reduce smear and hash, and made the presentation more open, so that would be number 2 in the list.
The mains cables and the filters in my experience also work well and have the same characteristics but perhaps less so than the Kinabalu and the Moncayo. I used to have a Linn LK140 and switching in 3 Jayas transformed the performance of the power amp, so I've never really gone back to anything else and continued to use it in my current setup.
It's perhaps less successful where energy levels are not so high and I've found that the interconnects and digital cable have less of an impact on sound quality compared to the links, speaker cables and Kinabalu platforms.
In my experience, music seems to be more 'alive' with the Vertex in place. Imaging is far better and there is an increase in quantity and quality of lower frequencies, and a sweeter top end. In systems that already have plenty of bass content it could actually overdo things so auditioning is the key.
Jeremy seems to sell quite a lot of this stuff and he's always been willing to let me try it out. In the context of high-end systems I'd say it's worth trying.
