I have the VBM Jr Double Boiler and recently added a PID to it.
W/out the PID, there's no such thing as temp stability. Fortunately
the PID kit is easy and cheap (under $200). You might want to read the
thread on HB. Once PIDed, its temp behavior is same as any other PID
E61 double boilers.
Other than that, due to its smaller steam boiler compared to any HXs,
the steam can't vigorously roll more than 6oz of milk at a time. But the steam
boiler will reach full capacity again quickly, maybe 15 or 20 secs, ready to
do another 6oz batch.
If counter space is not an issue, I agree, spend a little more and get
the full sized PID double boiler or Vivaldi.