Hi Ori,
I have the HP-B and it is too delicate for most of my uses, I tend to thin out my acrylic paints by 50 to 80% and still have difficulties with a constant flow of paint, it just gets clogged too quickly. Used with enamels, it would probably work better, as it is an artists tools meant to be used with artists inks. The HP-C is a bit bigger and uses (I think) a larger tip and needle, both of which should make it more usable than the HP-B.
The other consideration is the expense of the replacement tip and needle. My Passche VLS dual action, cost me $6 and $7 for the needle and tip. The HP-B replacement tip is around $45 CDN, not cheap!
With this in mind, I would stil suggest that you buy it, the control and build quality of the Iwata airbrushes is second to none, and if used with patience can be very rewarding.
Frank