I also have a Plantronics Discovery 655. Since it is my first headset, I have nothing to compare it to.

That said:

- the cylinder that you put the earpiece into is secure ... as long as you turn the earpiece in the right direction.

- volume was my main concern, and this set is plenty loud enough. I often have to turn it down a notch.

- there is a bit of delay, but I have no idea if this is the headset or the phone or their particular characteristics of meeting each other. The phone I use is a Samsung SGH D820 - also chosen for good ear volume.

- I like the size of the unit.

- There is a behind the ear "stabilizing" wire that you can put on. You take the silicone ear tip off, place a hoop in the wire piece over the ear tip post, then replace the eartip. The biggest hassle I have had so far with the unit is that ear tip can rotate quite easily to "unlock-remove" positions leading to it and the wire falling off in my briefcase or pocket ... or onto the ground.

- I do like that it is small.