There is seemingly a bewildering confusion of websites that I term under the general heading of penkits-dot-whatever, but there are two particular websites that are being confused with one another in this thread.
The one being asked about by Glen is pen-kits.co.uk - it is run by someone called Sam and his partner Rachel. Guilty of serial spamming on this forum, and although I may be wrong, I believe banned back in Jim's time, as they are similarly banned from at least two facebook groups that I know of. They keep no products whatsoever in stock, and when they have enough orders to justify a bulk purchase from Rizheng, that is what they do.
The other is penkitsuk.com - run by someone called Tony. Tony in theory is a member of this forum, but hasn't logged in since November 2014. They keep products in stock and I understand that some of their profit, at least on the face of it, is donated to charity. Their catalogue is also predominantly from Rizheng, but in their favour (I have no direct experience of their customer service) they do serve to make Rizhengs product easily available to all, without the perils of overseas shipping or import taxes.
As Derek has observed, if you wish to use inexpensive kits, you might as well assure yourself that you are getting the best deal in terms of price and customer service, and I pass the above on for information only. Each must make up their own mind from whom they wish to purchase pen kits.