Getting back to the Red Oak bull (instead of his former owner) - MD, you're correct in that I, personally, wouldn't use him. But, just because I wouldn't use him doesn't mean he's not a great prospect. "Prospect" being the operative word here. There's always a lot more great "prospects" out there than there are truly great proven breeding bulls.
And LFF, like you, I'd want to see some progeny data before I used him, especially on heifers.
Regarding Feltons 517, the subject of the thread and a great proven breeding bull, the "knock" that THG expressed on 517 is the SAME reservation that I've personally heard from several respected longtime breeders. I'm taking THEIR word on 517, not THG's. I've never seen 517 (and don't believe that THG did), but these breeders did and they have also seen the results of his breeding firsthand.
The 517 bull is said to be a good compliment to stout, muscled cows, which is his own weakness, if REA EPDs are to be believed.
Linebreeding 517 could be successful with careful selection, particularly guarding against setting in his own weaknesses, like lack of muscling. To be successful, I believe it would involve the use of ultrasound data and a person with a "breeder's eye" making the decisions. The result could be a herd of cattle that would add a lot of good traits to other breeder's herds.
George