Forgot to mention an important difference is in the deposits:...

Forgot to mention an important difference is in the deposits: HFR is all Sylvinite, but EML has a large Carnallite component (going from memory). I personally think that EML are going to run into major mining difficulties due to this. Carnallite does not make for a stable mine, and in a lot of cases solution mining would be the preferred way of tapping the resource rather than room and pillar with continuous miners. Not really a problem for Project O, or much of the resource for SHP as there are huge component of sylvinite to go after in the total resource, and probably a reason the Project O was chosen first.

Also EML is not just on AIM but also on the SETSqx section of the exchange, which does is not very liquid and many brokers don't support.