Well, racers on the ground and in the sky have trusted their lives to harness companies for decades.
Companies like Simpson, Crowe, Hooker and others have been in competition for market share and some have gained notoriety in certain segments. In aerobatic competition and in aviation circles, Hooker seems to have the lion's share of the business and has become the recognized "leader" in the industry.
Making your own is akin to sewing up your own parachute. Alot of expertise goes into a harness to make it safe, durable, comfortable and easy to use.
Why re-invent the wheel (or wing in this case)?
These harnesses have nice pads that are really comfortable on long trips and the rotary buckle, although PRICEY... is hard to beat!
Every time I strap into the Citabria (which has Hooker Mil Spec buckles) it makes me wish the RV was done just so I can use the rotary buckle!
That buckle, in and of itself is reason for getting in on this buy! It is SUPER easy to use and FAST!
The Mil Spec one is clumsy and ungainly. Albeit, it DOES THE JOB!
Besides, with a name like Hooker... you KNOW it can be trusted!

CJ