Here's all the difference
http://ceriatoneforum.com/index.php?topic=1471.0 Some say the 1st generation silver panel Dumble ODS's were the "easiest to play"
They have a very rich singing quality compared to with the Hrm you have to be a very "touch sensitive" player to get everything out of the amp .Both are great amps to play although. The Hrm is some what the most versatile of them ,all depends what your after (good clean,or good OD) The HRM can have both but in a very subjective way.All the different generation's of amps will definitely reflect on that final decision so I would advise you to listen to all the clips you can,and do some serious homework.These amps are capable of alot of genre's/style's.