These are needed if you're going to mount one of their heavier battery units on a 2 post rack. In my opinion, they should have been included with the original unit, or at least offered at a more reasonable price.
They are strong, and they do hold the heavy battery unit without any noticeable sag on a 2 post rack, unlike the mounts that were provided with the battery. The steel on these are about twice as thick as the provided mounts, and of course, they are 2U tall rather than 1U tall.
I hesitantly recommend buying them if you're not happy with the droop you have on the factory provided mounts.
Tripp Lite, please drop the price. It's just a little bit of steel, and it's solving a problem you created by including weak mounts with the equipment you're selling.