The more I've read and looked into this process, the more I would be tempted to try it, since, once all is said and done, the poster is not backed with any added, substrate layer, like masa-linen or paper backing.
The gel sizing is removed after (any) restoration or touch ups are done, and one can see/feel the back of the poster (or insert, WC etc), just like it was, prior to being worked on
In my experience, the attention to detail, as well as the gel resizing procedure of Poster Mountain, are much better than Lumiere's aka Mario Cueva's.
The backside of the 40x60 that Lumiere did is not close to the same as it was pre-restoration. Mario explained the process he uses, that is, he mounts the poster, then sands the back of it to remove all the residue. On my 40x60 (that I sold recently), it's fairly rough texture, and the poster is not completely even in thickness, as some areas were sanded more/less than others.
The 30x40 that PM did does not have that roughness on the backside. It's difficult to describe the texture. It's kinda like it has a very thin, even coating that makes the poster much more rigid and flat. Overall, it's much closer to the original, pre-restoration state of the poster.
Although this is not part of the topic here, frankly speaking, the customer service was also much better with PM.