I started going the Lavacore route last winter when I purchased the full suit to use under my drysuit in case of a flood.
I like it so much that I have almost the whole ensemble [meaning socks, gloves, hood, pants, vest, longsleeve shirt and full suit.] On hindsight I wish I had bought the vest w/hood since I use them so much. Because of my Alfred Hitchcock physique, I need to use suspenders to keep my pants up when I get out of the water. The material soaks up a ton of water and is about 3 times heavier when saturated.
Lavacore is not cheap. You will spend the same as a good wetsuit. The beauty of it is you don't even know you are wearing it and you can mix and match. It also goes well under a drysuit and does not add to the constriction like a wetsuit or snowmobile-type suit does. It's like wearing regular street clothing. If you seal up all the openings with hood, socks and gloves, there is no water circulation between the skin and material.
I have been using it all summer for shallow lake diving, an hour at a time. The temps were in the mid 70's most of that time. The thermocline in places is at 22' and drops 8-10* so I stay shallow and recover lost fishing gear for fun. It is in the upper 60's now and I have started wearing the vest. I think it is ideal for extended warm water diving. You can leave it on between dives and it dries out quite well. On the other hand it is slow drying overnight especially under humid conditions. It must be turned inside out and even then takes a couple days to get bone dry.
I would strongly recommend it in place of a wetsuit if you are doing a lot of snorkeling or shallow water diving above 68*. For a little colder than that I will be adding the full suit on top of the pants,vest and shirt. Any colder than that and I will get out the 7mm.