I've seen quite a few trees at local nurseries on this rootstock (Volkamer lemon ). I've haven't read much about it. Anyone have experience with it. What are it's characteristics?

Volk produces a scion with extreme vigor, very large tree size, very heavy crops of unusually large fruit. But the fruit may be somewhat "dilute" in flavor since most of the additional size is water. Also, the trees are not cold-hardy (similar to Rough Lemon). They are tolerant of the common virus diseases, but susceptible to citrus blight. So it's popular for the processing market, but not so much for fresh fruit production.

I've seen it on clay (acid) in Brazil, doing well, and it's ok here on neutral- to slightly-alkaline sands. So I suspect it would be ok, but not really certain of that.

Volkamer lemon is good tolerant to alkaline soils, but with very bad drained clay soils the rootstock won't grow well... because it often suffers from root problems in such wet soils... but on good drained soils, they grow very vigorous are a very good cropper.

In most cases, in clay soils, were often drainage isn't that well, the sour orange is the best choice, if the impact of CTV isn't limiting the usage of the rootstock.
If alkaline isn't limiting the rootstock choice to alkaline tolerant rootstocks, in such sticky, heavy soils, the best chioce is trifoliate orange...