Well...
Ill put myself out there a bit!
I used to refuse to take anything but a broadside shot STANDING STILL even on deer shooting under 150 yards with a 300 win mag.
Then I heard Larry Wysun (sp?) saying a texas heart shot was VERY EFFECTIVE.
Since then Ive probably done it maybe 8-9 times...only on deer... only with a 300 win mag (one time in Wisconsin with a 12 guage slug). ALL were bloody messes and all but one left the deer dead within just a few feet. The furthest Ive seen one travel was about 40 yards but it tried to get up when I got close and I gave it a follow up shot!
Sooo, Id say Im not opposed to it with a big damn gun on a deer or smaller!
Id never try it with an elk...not even with a 375 HH.
Now, Id say Ive had as many experiences with a head on shot on deer with the same guns... all of these were very successful. Put em down in their tracks... I dont remember any of them taking a single step!
Id take a head on shot on a DEER or smaller bear with a big gun!
THAT SAID...
Ive had several opportunities to disprove the idea of a head on shot with a bow

The 3rd biggest WT I killed in Mississippi was shot at 19 yards with a strong quartering to me angle and I would be ashamed to describe the details.
Ive done it a few times and its a shot Ill absolutely NEVER do again on any animal!
Ive seen that shot go bad on a damn 30 lb beaver at 30 yards shooting a 76lb bow and a broadhead!!
Its a NO GO on ANY animal!
as for a Texas heart shot... one of the 5 biggest WT's Ive ever seen was in Mississippi and I was at full drawn at 15 yards as it walked straight away... I didnt take that shot and Im completely ok with that!
anyone that takes a THS on any animal with a bow is a *censored* in my book!
PS....you can add the straight down / spine shot to that as well...always seems ok and probably is with a big gun... with a bow...its a recipe for a half shaft or less that misses vitals and leaves almost NO blood trail!
Ive tried it a few times on 60 pound Georgia WT's with about 80% FAILURE

The very first deer I ever shot with a bow I went for the spine breaker straight above from a tree stand shot... 14 hrs later I decided Id never find her without any blood....
Some would say Ive had a decent year...
12 or so pigs in Georgia ranging from 20 lbs to over 250 lbs
a 4pt mulie in OR
a 5pt rosey in WA
all ended great...100% recovery.... all went down very quick and left HUGE blood trails! some shot as far as 52 yards out....
why?
Im not a great hunter nor an amazing shot!!!
all exactly broadside or quartering away!
all shot with a virgin broadhead (never touched anything but a quiver and even that was done gently!!)
marginal shots are the stuff "almost got him" stories are made of!
an intentional bad angle shot that ends with a wounded and not recovered animal is a badge of disgrace that ALL hunters should strive to avoid!
IMO

I pissed off a guy in oregon last weekend because he was about to take a bad angle shot at 48 yards on a deer through a thread the needle opening ( Iwas helping him try to get his first bow deer).
I dont know anyone that could have pulled off a happy ending with that shot...
it meant he got no shot...and for that...Im an *censored*!
Im ok with that!
now...Ive gotta go find me a bear!
dave