Hi,
The TV Radians are excellent eyepieces. The later series are very marginally better than the early Radians IMO, although its exceptionally close. They have slightly better coatings than the earlier ones IMO. That having been said I would be very happy with either and it's not a deal breaker.
I have an 8mm (late version) and it is about the equal of my 8.5mm Pentax XF.
I also spent a lot of time (several nights) comparing a 6mm TV Radian (early version), a 6mm TV DELOS, a 3-6 Nagler Zoom, a 6mm UO HD ortho and a 7mm Pentax XW in both my 10" and 14" Newtonians.
The 6mm Radian held up very well and while overall it was probably just a spiders hair behind the 6mm Delos and the 7mm Pentax XW I felt in a couple of aspects it was better than the 6mm Delos. Notably it's off axis sharpness when used in my 10" Newtonian, without a paracorr and its ability to baffle internal reflections. Overall whilst not the winner, I felt the 6mm Radian was an outstanding eyepiece, which I would be very happy to own, if I didn't have the 6mm DELOS. I am sure if you get a 3mm Radian it will be just as good as the 6mm.
Now your going to ask, how do you tell the early version Radian from the late version Radian
I have attached images of both in 6mm. The later version is on the right and has no "knurling" underneath the green lettering, it is smooth.
You would also be very happy with any of the premium 3.5mm eyepieces like the 3.5mm Pentax XW, or the 3.5mm Vixen LVW. The 3-6mm Nagler zoom while very good on axis doesn't have the eye relief of the others and its off axis performance isn't as good as the others either.
Cheers,
John B