Hi Starkiller! I like to think of myself as this forum's resident thin neck guru, I have all three thin neck sabers and I'm a HUGE fan of SaberForge's thin neck design. All three of the thin neck sabers (Redeemer, Prodigal Son, and Exhalted) are built for full speed, full contact dueling, just like every other Elite saber. I have dueled with all three of my thin necks, and they all hold up extremely well in heavy dueling. I haven't had any issues (as a note, the Crystal Reveal versions of the Redeemer, Prodigal Son, and Exhalted are NOT warrantied for dueling and should not be dueled with).
One thing to consider is that the activation box on the Redeemer and Prodigal Son can get in the way depending on your style of dueling. If you're going to do a lot of spins and twirls, it can be difficult with the activation box. That's why I personally love the Exhalted, it's my go to dueling saber. It retains the beautiful design aesthetic of the thin neck, while having a clean body with an excellent grip and no activation box. Furthermore, if you're set on either the Redeemer or Prodigal Son hilt, you can always order them without the activation box! The holes for the activation box are predrilled into the body of the hilt, but you can always cover those up with two 8-32 button head screws.
If you're interested in seeing a stress test of the thin neck saber, you can check out my youtube review
here. The durability test begins around 3:30. I use my Redeemer and smash the blade several times onto a metal chair in my garage
Regarding dueling with other crystal sabers like the Monarch, here's what Phil Isherwood the owner of SaberForge said just earlier today on a Facebook group comment:
"You can duel with the gladiator, descent, and monarch, those are warrantied for blade on blade full contact dueling. The spring loaded reveals are highly detailed with a lot of moving parts and should never be dueled with."
Hope all of this helps! Like Silabus said, even if you get the ugliest and most basic hilt SaberForge offers, you'll be extremely pleased and satisfied with your purchase
Good luck making a choice! They're all so gorgeous!