Received a Hydra in today's mail.
The finish appears identical to the XM-3. Not positive, but pretty sure it's not HA3...at least not like any of my other HA3 lights.
Hydra's differences from the EL XM-3:
...body tube has no clip, or holes to attach one.
...the tailpiece is 3-4 mm shorter with recessed reverse clickie swith.
...slightly stiffer spring.
...the reflector is more shallow, without a polished finish.
...there appears to some sort of "optic" over the LED.
...no fiber donut to protect from reverse polarity.
...the back of the circuit board appears to be more crudely crafted.
Now the part that counts (IMHO), the beam: They're very similar...but
My eyeball assessment (with new AA's in both) is that the Hydra's beam is "brighter and whiter". Though the spill (outside the hotspot) is dimmer with a couple of not too noticeable rings.
I've always liked the rugged case of the XM-3, and that it uses AA's. However, all six of the XM-3's I purchased have a slightly greenish tint.
The Hydra's is white (at least this one is).
If you're in the market for this type of light, the Hydra appears to be a viable alternative to the XM-3.
jb