I've owned a Dragon's Wing and a Spyder (I currently own a Series II Entwistle replica - you can view the build thread in the factory to customer section, or you can look it up on the main Alembic page where they talk about custom inlays that are available). What I would tell you is this .....
First, the Spyder tribute basses are a lot different than my Series II, aside from electronics and hardware differences. First, the body on the Spyder is not the same as used by Entwistle. The neck joins the body farther up the fingerboard, making it a loooonnnnnngggg reach (for me anyway) to the first fret. On my Series II, that isn't the case, making it more comfortable to play either sitting or standing, for me, anyway. Also, my Series II is more pinched at the waist of the bass, making it slightly lighter than a regular Spyder.
Playing a Spyder seated is no different than any other bass, I guess, although the reach to the first fret, as noted is a long one. Standing up, as long as you have a nice wide strap that grips (I use Moody Straps), weight is no issue. Or at least it isn't for me, anyway. Also, when standing, you have to remember that the front strap button is located on the back of the neck just under the upper horn, meaning that it will lean forward a bit. However, since one's elbow will be on the back horn most of the time, it pulls the bass back comfortably. I have no problems playing my Series II standing as a result.
I haven't seen many come up for sale too often. I sold my Spyder years ago as my Series II was being built. Hope you can find one.
Alan