There are more third-party tests for Nexa than any other vendor. But due to
intra-batch variability, including recently with
Nexa reta (R12 in July), the ideal is testing one's own kit, which is affordable for those already paying $600+ with Nexa.
I have gotten domestic reta (R50) for about 60 cents per mg, shipped the next day by UPS (from a group-buy group that was selling in-stock, leftover reta kits). But most people buying from GBs, including myself, are comfortable enough with the GB testing and don't test their own kit.
From what I read before, SRY has been relatively good with their US warehouse, compared to SSA, for actually shipping from the US. And I didn't have a problem with SRY domestic, but I only ordered twice, and they were not high-demand GLPs.