My brother-in-law has a Turkey fryer and it does turn out moist and delicious from it. But I would not say it is better than a TBE Turkey...
Sure a Turkey fryer can cook a little faster(7 minutes a lb and 10 for TBE) but it takes at least 30 minutes to bring the oil up to temp meanwhile a TBE is ready within a few minutes.
You can put rubs on the fried Turkey but as soon as you drop it in then the rub comes off...TBE the rub stays on the skin.
Cleaning a Turkey Fryer is not fun. Disposing or storage of the oil is a real pain. When you are done with TBE just run it for 15 minutes to burn everything, scrape the bottom of the cooker, and then dump the oil catch...very easy.
The TBE and SRG are so versatile. You can cook ribs, chicken, fish, steaks, and even bake in the thing. Try that with a Turkey Fryer.
I cannot recommend these cookers enough! If you do not have one you should. If you do and have not I hope to change your mind