I've ordered directly from them and contrary to what some people have said they do not have minimum order requirements and will sell to private individuals.
However, it has to be said they are hard work to deal with. They are not really geared up for selling to consumers. In particular they only have one payment method - wire transfer in advance.
But as you say they sell stuff that you just can't get elsewhere so the hassle is probably worthwhile.
Not surprisingly their prices are also much lower than Happ's and Ultimarc's. But bear in mind that unless you live in Spain you'll be paying currency conversion charges, possibly sales tax, possibly customs charges, and quite hefty shipping charges.
I am lucky enough to have a relative who lives in Spain so I could avoid most of the aforementioned charges.