As an avid handcyclist, I can tell you this is NOT a stable/safe design. I've got the scars to prove it. This configuration only gets more unstable as you place more weight on the trailing two wheels (aka: lean backwards, as is natural) and will start to swing from side to side, eventually throwing you and the bike into a side roll. A reverse trike configuration is the best design choice, due to its inherent stability, even at high speeds, because as you lean back on the drive wheel it increases in stability.
This handcycle is a delta trike aka "reverse trike" a trike is a tadpole trike. I think you are thinking that a tadpole trike is safer than a delta trike.
The "struggle" is not with the low center of gravity, but the fact that you've got muscle groups that were never designed to motivate your entire body weight, plus a bike. Simple physics; Bigger is stronger. Been handcycling for 10+ yrs. now and put on over 20K miles on various handcycles.
