I got the chance to use the Zeagle Sentinal octo on my trip to the Flower Gardens off of the Texas Gulf Coast. My regulator was in the shop and since Harold the Shop owner has the same thing I do, he lent me his rig. His setup had the Sentinel, while mine has another TX50.
Typical depths at the Flower Gardens are 80-90 feet. And while at this depth, I did do a switch to see how the Sentinel compared to my Zeagle Tech 50D (essentially equivalent to the Apeks TX50). I was pleased to find out that the Sentinal performed a bit better than expected for that depth. While it did take a slight bit more effort to draw a breath at 80 fsw versus my primary, it was not a major significant amount. And I had absolutely no free flow problems during entry (giant strides from 7-feet!) nor any other common octo problems.
So my "dos centavos" worth is that this is a good choice for an octo for use with purely recreational diving. However, if you ever see yourself doing stuff beyond that (say 100 feet or deeper, overhead environments, deco diving, etc), then I'd do what I did and select a second TX50.