Ok finally had a chance to use it last Thursday.
For a review of how the strap and packaging looks like and how it functions please refer to the wonderful write up by Rubber_Duck on the first page. My usage of the strap was abit more specialised - I purchased it specifically to hold my 7D (with grip) and a 300/2.8.
Some points on the above rig:
1) I confirmed with the Custom SLR sales team before I attempted it; they confirmed that they had extensively tested their C-Loop and split strap on a similiar rig with no issues noted. I carried the rig for 3 hours last Thursday - no issues encountered by me either.
2) Whilst it does not take the weight away altogether; it appears to distribute the weight across the shoulder nicely so that your shoulders do not feel the stress from the pressure exerted by the strap. Its amazing what that little slit in the strap does. Again this was consistent with the feedback given to me by the Custom SLR sales representative.
This is a picture of how I set up the C-Loop and Split strap (taken with iphone downwards; apologies if my belly is in the way - I already sucked in as hard as I could hehe)
The 300/2.8 is attached to a Really Right Stuffs lensplate which is in turn connected to the C-Loop and strap. I know alot of you might point out that its quite dangerous as the lens plate is only attached to the lens collar by a single screw whilst the C-Loop is only connected to the lens plate by another screw. I'm no engineer but I know it takes alot of force to break a screw off (definitely much more than what the weight is exerting). I trust the manufacturing standards of both the RRS and Custom SLR. Its all in the mind sometimes.
The ability to take off/attach the strap from my lens is important to my shooting style and requirements. With a little critical assessment you should be able to determine if the Custom SLR offering is for you. As far as I'm concerned I am confident its carry capacity is no issue and its ergonomics does helps the photographer deal with the weight of whatever's attached.