I've used a weems & plath and have a plastimo puck. Great for RC work. One subtle difference between the two: the plastimo is designed to be held close to your face to be able to read the prism (but optically it looks further away, so reading glasses not needed, I think.) while the weems & plath is designed to be pulled away from your neck and held a few feet away pulling on the neck strap.
I think both designs work well enough, but it can be a surprise when switching from one to the other. Very happy with my plastimo to save $$$.
I think both designs work well enough, but it can be a surprise when switching from one to the other. Very happy with my plastimo to save $$$.