@Kermee Agreed, it was a very smooth process for me as well.
Migrating from the 3100 on our 250/250 + 5G Internet connections, I find the 4200 waaay over-powered with a CPU load ~3% where-as the 3100 was steadily around 35-40%. The two remote offices still on 3100s will receive 2100s to keep the costs reasonable.