First congratulations for a great product, I enjoy using HCE Mac (Yosemite).
May I add a couple of suggestions that I think would further improve the product. I apologise if these have already been suggested, or I have missed the proper thread.
- Arrows. Ability to show the current best move, or ideally from top X PVs, as a set of arrows on the main board. This would be similar to that provided in Shredder GUI, Fritz GUI, etc.
A very good example is the implementation in the popular site http://analysis.sesse.net which display different grades of arrows. Another good example is Chess Tiger on iPad / IPhone using a similar arrow grade system.
I find this helps giving an immediate assessment of a position, when using an engine and when fast forwarding through games - rather than looking and having to interpret on ‘the fly’ the PV list.
- Game Profile, e.g. similar to Shredder GUI, Fritz, Smallfish (iPhone), etc.
I find this a really nice way to get a bird’s eye view of the main interest areas within a game, and to quickly home into these areas.
Maybe also (like Fritz) combine various engine parameters (depth, evaluation, etc), although not so important for me.

Another couple of nice to have suggestions:
Full screen mode, similar to other standard apps under Yosemite (although I presume you may be tied to what the QT framework provides here).
Hide Tool Bar: option to possibly hide the top toolbar.
If you can get the first two suggestions implemented, I will buy you a few rounds of German beer !
Cheers,
Mark