Currently, I own the Ultra, the XL+, and an AXE FX III.
I had sold my original Ultra when the AXE FX II Mk I first came out and I regretted it since the Ultra sounded a lot better to me for a long time (all my Ultra presets had been tweaked to what I liked for recording) but eventually the firmware updates for the AXE FX II improved the unit.
At some point I found that I really liked the AXE FX II Mk I and I stopped missing the Ultra
I had purchased an FX8 to go with my JMP-1 for my live playing and I had learned a lot about the effects in the FX8 and scenes so I decided to get an XL+ and it replaced my FX8 in my live rig.
I found with each firmware update that the XL+ kept getting better and I was telling a friend of mine how great it was for effects and recording (I tried using it to replace my JMP-1 for playing live but I could never get an XL+ preset that sounded and felt like a real tube amp going through my Marshall EL34 50/50 tube power amp and Mesa cab).
Well, my friend wanted to get an AXE FX but he had limited funds so I suggested to him to get an Ultra.
He bought one but needed a LOT of help setting it up, connecting it to the computer, creating presets, etc..., so I had him leave it with me to get it dialed in for him.
I fell in love with the Ultra all over again for recording and playing through my recording interface and speakers (in part, due to Leon Todd's Ultra presets paired with the Own Hammer Mesa cab).
The OH Mesa cab opened up the Ultra for me and it made it a LOT easier to get GREAT sounding presets that I could use for recording.
I remembered there was a certain feel, tone, and uniqueness to the Ultra that I forgot about since many years had passed but the joy that I had felt using the Ultra was coming back (and then some).
It was also a lot easier to use for dialing in a live sound that it was in the past (I am sure that I picked up a few tips, strategies, and tone-shaping ideas from these good souls in the Fractal Forum).
I ended up buying three Ultras since one is for playing live (I have some GREAT presets for live playing now), one is a back-up, and the other is meant to be left at our studio for recording.
I will always keep at least two of the Ultras since they sound different from the XL+ and the III.
Yes, there has been a lot of improvements that you can find in the XL+ and II but I feel there was something lost in the XL+ and the III that was GREAT in the Ultra.
All three units are unique with different tones/feels and great in their own way and if you can find an XL+ for around $1,000 then I would say get it but the Ultra is more affordable right now and you can find them for pretty good prices (you will need a headphone amp like the $23 Behringer MicroAMP HA400 4-Ch Headphone Amplifier and a $29 midi interface like the M-Audio Uno).
I recently learned how to dial in ALL of my AXE FX's for a live sound where I always failed to get one in the past but the simpler structure of the Ultra helped me to better understand how to dial in various things a lot easier to get that live sound for each of the AXE FX units that I own right now (for recording it was always easy) just like the FX8 helped me to better understand the effect layouts/options and scenes.
I was playing my Ultra right at this moment and then I remembered seeing your post and I thought I should provide you with a reply/feedback/suggestions and some video links for the Ultra (I put these together to show the wide range of possibilities for the Ultra):
Here is a link to hear "some" of the Leon Todd presets (I have a LOT of his presets for live and recording):
Here is a link to hear "some" of the Mark Day presets (I have a LOT of his presets for live and recording):
Here is a link to hear some others using the Ultra:
https://www.youtube.com/watch?v=rbWj3x0VTWU
https://www.youtube.com/watch?v=ydx18i825ug
https://www.youtube.com/watch?v=gyvr26z0Mbk
https://www.youtube.com/watch?v=dGJvcs8Gfog
https://www.youtube.com/watch?v=UVuDsDfrlPk
https://www.youtube.com/watch?v=Jm4SlcgE7qg
https://www.youtube.com/watch?v=hUfV1fvziso
https://www.youtube.com/watch?v=CCe0fZ1rKqA
https://www.youtube.com/watch?v=K1h-1_eeIBo
https://www.youtube.com/watch?v=rqB2HoBLDuo
https://www.youtube.com/watch?v=WuPAbAlvnI4
https://www.youtube.com/watch?v=W0T-NpCWHrY
https://www.youtube.com/watch?v=fkxH3zTn5DU
https://www.youtube.com/watch?v=6g1YYTMBgHs (Reamping)
https://www.youtube.com/watch?v=wMc6rURackE (The Standard but you can see the AXE Edit being used here)