Hi,
Pretoria Eyepiece:
I recall them being talked about in the late 80's but I have never seen one. I don't know anyone that has ever used 1 even. It does get a very brief mention in Telescope Optics by Rutten and Van Venrooij, but they don't go on to say whether it works or not. Paraccor sounds a lot easier to me
UO 2.8X KLee Barlow:
I have used these a few times. They are light and very sharp on axis with good light transmission. It has a small clear aperture of only about 19mm and can vignette with some widefield eyepieces particularly with focal lengths over about 20mm. Eyepieces like the 19mm Pan, 22mm Pan and 24mm Pan all struggle with it. If you only plan to barlow shorter focal length simple design eyepieces, like plossls and orthos it's a really good barlow.
CS-John B