ES not great on all but the power tune (imo) but easily remedied with some customization by means of buffer.
Power tune (not really a power tune per say, just another tune imo) with the best ES of 17 fps has an efficiency of ~1.25 FPE/CI...not shabby. Need to know its true plenum volume to determine exactly what that is...I guessed at around 7 cc's total plenum volume. At that power level (42 fpe), with the barrel length this rifle supports (22.75"~), and the pressure it was shooting at (2700 psi), well, in respect to that, its quite bad....but thats due to that incredibly small plenum volume that likely sees a pressure drop of well over 1000 psi during its shot cycle...as opposed to one that is twice its volume seeing only 500 psi, or quadruple its volume while only seeing 250 psi drop (much more ideal)...
Ultimately, that pressure drop equates to much less average pressure at both the valve seat, and behind the pellet as it travels down the bore...its detrimental to performance to have such a small plenum volume...such a feature rich gun to have failed there (imo).
The good: Ultimately, you are getting a lot of gun for 300$ with this package. Large range of adjustments, some of which unheard of at this price bracket. 4350 psi rated. Side lever.
The bad: Small plenum (way small) which is severely limiting on lower pressure tunes. In its current form, unmodified, you absolutely want a high pressure (4350 psi) capable fill source, as filling to only 3-3.5k will provide quite lackluster shot counts compared to whats seen here. No appreciable baffling/moderator within shroud. Possibly lower quality parts through-out that would benefit from replacement/reinforcement.
I would recommend these in a heartbeat for an entry level, or tinkerer gun. If they had just given the rifle a good plenum and a valve buffer to help the es, this thing would be valued at well over 1k and still be able to sell for sub 400...ah well maybe the next iteration...but as far as this one goes for 300$, I approve.