I think they are a great idea having built several for my shops and garage. As long as they are used within reason*. The loading is theoretically split between the cleat on the wall and the outboard support.
Generally 50/50 of the load is on the wall and then hanging from the ceiling - all depending on where the load is concentrated on the shelves.
My opinion is getting a solid connection to the chord is the biggest issue. I would not use lag screws personally. Deep #10 deck screws or GRK framing screws.
Agreed. There are situations where these types of things can't be avoided. Anything to spread the load across ceiling members or to put the load on top of the ceiling vs. a bottom chord of a truss, etc. will help tremendously. So, adding members to spread the loads across ceiling components is good - or even better to run the cables/attachments up to to the top of the roof to purlins that sit on top of the roof structure/trusses where they are strong.
I've also had some success with this type of shelf:
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It is strong enough for me to do a pull-up on, but it only attaches to the wall. The advantage is that there is 100% clear space underneath. (No brackets or stanchions.) The disadvantage is that some of the shelf space is lost up top for the bracket/lever support.
I have a place where I have concrete walls that jut out at the top of the ceiling, so I was going to loose this space anyway. I was making a light well, but it turned out to be super-strong. In other areas, I fired the support out from the wall with lumber to match the profile. I just have small "straps" of plywood connecting the ladder frame shelf to the top supports. (I then have drywall hung over the straps to make it look like enclosed wall.)