HEI is High Energy Ignition, and while trademarked by GM, it now describes any system using a low-ohm coil for greater spark energy and electronic dwell control. A feature of these is no inline coil resistor wire (pink in Fords) or ballast required, with the module controlling coil current instead. The term includes coils under either 1-ohm or 0.7-ohm, depending on who you ask. This is the "HEI" designation, and it likely uses a GM HEI 4-pin module, but could also be a Bosch BIM 024 equivalent. Either module type is robust, even most clones.
HEI terminology aside, the housing appears to roughly be an MSD Pro-Billet clone with 2-screw cap. Without looking inside we can't know if it is a clone internally or not - but by the cap height it probably is
similar. My view on this is that it's an import copy of one or more systems, and has the typical pros and cons of them. It's a crap-shoot. Could be awesome, or trash, or in-between. From what I've seen, the price means nothing relative to quality. It is listed at roughly half the price of an MSD Pro-Billet equivalent, but with fewer springs and bushings, and perhaps limited or no instructions, warranty, or support.
If it makes you feel better, the MSD (if that's the type it is) uses Ford DuraSpark triggering mixed with a GM-style advance mechanism (below) that is easier to access for tuning. If you get one, I'd suggest confirming the return policy, so you have options if quality or fit is a no-go. Post-up if you get one!
[EDIT] Looking at the seller's other stuff, he is selling the big cap HEI at about 4x the price of others. This could be because his are better, or he has more bills to pay and whats you to pay them.
Without more info or an example, I wouldn't be able to tell.
