Pros - Superior detail, not real picky with amplification
Cons - The included hev70 is not up to the task
The he60 is the affordable version of the Orpheus, often referred to as the 'Baby Orpheus'. This is mainly due to the lack of a real amp, and the (supposedly) lesser quality as compared to it's sibling the HE90/HEV90, which sells for >$20k, based on recent sales.
Personally, I think there are better amps than the hev90 (eXStatA, Blue Hawaii), but ANY electrostatic amp is better than the hev70 - literally.
So, let's focus on the he60. When driven by a capable amp (which excludes the hev70, and almost all Stax amps), this phone is unparalleled in detail and speed. Often, electrostats are noted to be bass shy, but not the he60, and it's closest rival, the Stax Omega II. In the electrostatic world, there are few choices, and fewer still flavors. Those who tend to like the OII are generally not as fond of the he60/he90, and vice versa. Personally, I find the OII too dark, hard to fit, and generally not at all to my taste, where as the he60/he90 is more voiced for my listening preferences.
The he60 can scale up to any amp and source thrown at it, and is relatively affordable when available, which cannot be said of the he90. One mod that is de rigeur would be reterminating to a Stax 5pin (pro bias) plug, as the hev70 connection is in no way compatible with any other connection.
Regarding amps, my personal favorites have been the KGBH and the eXStatA, where the KGSS, Woo GES, and anything manufactured by Stax (252, SRM T1, 727, 717, etc) I simply found lacking. Some of this may well have been that all standard Stax bias is 580v, where the he60 is 540v, but hybrids are definitely my strong favorite ofer SS, wrt electrostats. There is a warmth added to the clinical tendancies of stats that add just a touch of flavor, but not coloration.
In a nutshell, these are out of production, some parts are no longer available (earcushions for one), and appeal to a subjective preference in tone. If you are a Senn fan, you will note the signature from it's cousins, the hd600/650/800, and yet, note this can reproduce signal like they just can't. That said, they simply cannot transfer bone jarring bass like the hd800, and require a dedicated electrostatic amp.
If precision is the game, the he60 is a player. Electrostats are different, and you better be prepared to invest in the chain that goes with them, otherwise, temper your expectations.