[time-nuts] Confusion over Thunderbolt - noob is going crazy

[Taka Kamiya]

I hope I don't get yelled at for asking this question.  I honestly looked everywhere and still can't get this.
I have several GPSDO but I don't have a TRUE Thunderbolt.  I want one.  So I started looking.  There seem to be infinite variations of them.  So far (I have been looking for a week), there are no good summary (or even a summary) of various types and how they are different.
I know there is a thin type that looks to be 1" or so thick, and thick type that is about double that.I know thick type can have blue label with current Tbolt E, or red label (read somewhere this is an earlier one?)
I know there is a type that contains inferior oven and better one.  (Marked Trimble)I know there is a type with F connector for antenna, and there is one with BNC.I know there is an early type and late type.  (I don't know how to tell)I know the latest one is T-boltE, which is not necessary similar to earlier ones.I know there is a type that requires single voltage and 3 sources.
What I don't know is:
How many different types are there.Any particular one to avoid?  I know there were some experiment done with replacing OCXO of earliest type.Why form factor change?  OCXO does not seem to be any taller....Spending $1500 for new one is out of question, but price seems to vary from $150 to $500 for used ones.  Since most of them come from China, I'd think they are reclaimed equipment.  Is this assumption right?
Any reliable source?  I am a bit skeptical with the market the way it is.Are they all telecom quality?  

Thank you very much.


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(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG