Unlike the other two posters, I have in fact made it.
It's the best tasting turkey I have EVER eaten, anywhere, period. The meat is amazingly flavorful, and easily the juiciest I have ever had. It's like nothing else, and I highly recommend trying it at least once.
I would rely on a thermometer before relying on the times indicated. Cook until the breast hits 165, the thickest part of the thigh 175, and the stuffing 165. NB: You will lose turkey skin, possibly all of it. If this happens, you will have the absolute ugliest Bride of Frankenstein turkey you have seen in your life. Not that it looks good when you take it out of the oven or anything, but a skinless turkey is just plain hideous. I think it would help to baste it just a couple of times (if at all) and let the coating get really, really black. When we basted it as the recipe described, the coating never got really black and hard, and I believe that was the skin's undoing.
There's a very funny and detailed essay on this legendary turkey in Jeffrey Steingarten's first book, "The Man Who Ate Everything". He offers important tweaks to the recipe which should help. The thick coating of flour paste (provided you make 3 times as much as the recipe says, according to Steingarten) encases the bird in a hard black shell, discarded before eating, that holds in moisture. The 5 hour baking time is probably a way to insure that all that stuffing comes up to a safe temperature. I'm can't wait to try it, but not this year.
The rest of the Steingarten book is a great read, by the way.
Basting a turkey is a sure recipe for dry meat. Opening the oven door lowers the temperature and lengthens the roasting time. The proof: this recipe says to roast your bird for 5.5 HOURS!!!
And basting it every 15 minutes . . . you'll be using slices of the breast meat for roof shingles.
You don't need a lot of fancy technique with a turkey. If you just stick it in the oven, on a rack breast down, and forget it, it will take much less time and be so moist that the breast meat will squirt you in the eye when you stick a fork in it.
I like the "breast down" technique, too, although I rotate the bird once, browning first the breast, and then each side, before leaving it on the breast to finish cooking.
This year I will probably stick with brining and smoking an unstuffed free range bird in a Texas-style offset smoker using natural charcoal and cherry wood. This worked very well last year plus made the annual juggling of the side dishes much easier.
We do a roast beef every year because one of our sons refuses to eat bird meat of any kind, and it's a holiday, so I like to make everybody happy.
But there's just something ridiculously Quixotic about the Thompson Turkey recipe that calls to me. ;^)