I've read good stuff about Soundsmith, but their cartridges are quite expensive when delivered to my door in the UK, about £300 (this price includes shipping and VAT, but there may also be duty and UPS brokerage fees to get it to my front door in the UK). There is then the question about any warranty support and having to send it back to the USA.
The UK sellers are about £270, but I've not seen many reviews about their cartridges. Anybody here bought from the UK and if so, were you happy with your purchase.