Hi Dan
I have tried Lavacore tops and so has Maribi. I will be a dissenting voice here and say that I was not too impressed, and actually found them far inferior to a properly fitting 2 or 3 mil wetsuit. They can feel tight and snug when you put them on, but they get baggy when wet. They let water in through the neck and wrists (I did not try a fullsuit and so cannot comment on the ankles). They will never give the skintight fit, water seal and and streamlining of a wetsuit. Given that I do not need any extra weight with a 3 mil (with my 6 lb plate), the issue of extra weight is not a negative and the positives far outweigh. Also, I do not have confidence that these materials will last as long as a good wetsuit (ie many many years).
They can add some warmth, and Maribi puts her top under her wetsuit in the winter, but she says it does not make that much difference, and she will probably add a 5 mil wetsuit this coming winter, like I did last year. If you are diving tropical waters, the little warmth they add is fine, and they do offer scratch protection and have benefits on the surface. But, from what I have seen, a good wetsuit is a far better choice. You will see me in my 3 mil this summer.
Now, I will say that we have wetsuits with an unbelievable set of sizing options and multi-panel construction(Waterproofs) which give us a skin tight fit very close to custom. Maybe wetsuits with more generic sizing do not compare as well, but I still think the wetsuit is better. The high cost of these "tech" materials also makes the choice of a wetsuit easy.