(general comments not aimed at MA)
Choking and retrieving a lanyard and lifeline are an essential aid to secure working in trees. Using a micro prusik of high strength, high modulus fibres does not enable this, unless the lanyard is passed back on itself (like a timber hitch) to clip the pruik. And doing this is the same alignment on the krab as just choking without the prusik anyway. A RG on a lifeline is limited to small diameter timber, and cannot be safely retrieved from the ground by use of throwline when used in this fashion on pole work.
The durable safety of high modulus prusik cords is highly questionable (see below), and even the open gated strength of a correctly choked krab is superior in reliability. The way high loads come on the line in a correct choke also rolls the gate away from the wood, so its not a practical issue. Again, if worried use a steel krab, or short round section alloy krab with a high strength barrel such as the Ovalock (why do you think the ovalock exists?).
http://www.caves.org/section/vertical/nh/49/cthsc/cthsc.html
Karabiners used in industry will typically have a minor force pushing on the gate (resting against walls/wood/rock). That doesn't mean all work at height must use shackles instead for obvious reasons.
Work positioning forces are 6kN MAX. Look at the gate open strength of your krab. Worst case scenario it can handle it. Only an idiot (IMHO) would think they are going to work at height expecting 5,000lb forces! Thats just a safety factor to cover the less than ideal wear and tear circumsatnces all work at height encounters. durable safety (and strength vs security) concepts again.
For lanyards, Micro prusiks don't solve this one and have real risks of their own. Correctly choked Krabs do solve security issues and are not a real concern in work positioning scenarios.
