I've used them a few times in the past m8 with no problems whatsoever.
Both Paypal and Nochex were on a par with each other a few years ago, until ebay bought paypal and it became the "default" auction payment method.
Nochex used to only accept debit cards, ie not credit cards so I suppose that may have held it back a bit.
I suspect that the fees are less for the vendor using Nochex too, that will be why he prefers it.