I have to say that based on dimensions, the REI is the better option for chefisaac because of his height.
However, I am not a fan of tents that are complicated by having more poles than they need. The REI, judging by the pictures, has a couple more poles for the "vestibule", and those add weight and the possibility of being lost.
The Helleberg misses out because there would only be six inches of space between head and toes and the walls when chefisaac is stretched out, even less if he points his toes in a big stretch.
Other differences that I think I see between the two is that the Helleberg is a four-season tent and the REI a three (and unless you intend camping in high winds and snow, then the Helleberg is overkill); and the mesh inner on the REI, which does have its advantages so long as the outer also is adequately ventilated.
I should point out that in most circumstances where we or I have camped, freestanding is not a particular issue. In all the nights camping out with both freestanding and non-freestanding, I think I have had to "freestand" three times. We currently use a tent similar to the Hellleberg without the big vestibule, and there have been no issues whatsoever with it -- in fact, it's probably a tad faster to erect if we are inserting the appropriate number of pegs for each tent.
REI also has a good reputation as a seller, although I've never used them except to wander through one of their stores on a previous trip to the US.
So, that's it from my point of view. Yes, go and sit and lie down in the tents. Don't be embarrassed by the idea that people might be looking at you. Just loll around. Sit up, take your pullover off and put is back on, even borrow one of their inflated demo mattresses and put it in the tent.
You are starting out with touring. When I started back in 1997, I bought a $45 two-person tent from a camping disposal shop and it did me for a trip across the Nullarbor and much more.
Then I bought a tent similar to the REI on, but with only two poles, and that did me for more than 350 nights of sleeping out. It sort of started to wear out, and was only a two person.
The current tent has done us for well over 100 nights; it is a T3 without the big vestibule.
The worst conditions have been handled by all of them, including below freezing, prolonged heavy rain, and wind in the 40mph range.
I think with REI, you will likely get quite a few years service, and be happy.