RAW and Mac1 hamsters
I have used both of these and found both of them to be very useful for different reasons.
The RAW hamster may seem expensive but it has a very clever feature that you cannot see in the pictures: both rotating shafts have "clicks" or "indents" that you can feel and makes the adjustment process easier as the clamp does not need to be completely released or excessively tightened between adjustments. These "indents" resist movement very well once the clamp is tightened.
The Mac1 hamster does not have the "indents" but it is available with 2", 3" or 4" pivoting arm lengths. This flexibility allows the shooter to match the hamster to the particular rifle setup, balance and personal preferences.
The RAW hamster uses 5" pivoting arms that may be too long for some applications. I have requested them to make a 3" version for me.