I hauled hundreds of miles with a two horse straight load when I competed in endurance. Always had something to eat in front of my horse and never had an issue.
A horse can choke anytime anywhere.
The only issue I have personally seen with a front load manger is a horse rearing up into it and getting stuck. Took 6 or 7 of us to dislodge a horse that had got himself stuck up in the manger after a horse show.
Bottom line - horses are continually finding ways to hurt themselves. Just because one person/horse had or did not have an issue doesn't mean the next one will/won't.
^^^ Happened to me, but without front mangers. Front was just open, with a door on each side. Horse reared up and went over chest bar, which was then on his manly area... his back legs didn't touch the ground, his front end was curved in the front area. It was a nightmare... Tried to take out the chest bar, but got one pin out and the weight of the horse made the bar go crooked so that we couldn't get the other pin out... and my dad almost broke his arm in the process. Horse got tired and eventually fell FORWARD into that tiny area... the door in front of him no longer opened (not sure why, rust or??? Was just borrowing it from a friend) so we had to pull him out backwards, through the other side (front) door, and if he had shoes, he wouldn't have fit (as it was we had to scrape off some hoof to get him out!). Would having mangers helped? Who knows! I just made sure when I bought my own trailer, there was NOTHING for him to get caught on/in, I bought a slant with no mangers ect... Sure didn't want to go through that again!!! Other than a little scrape, horse was fine! NOT easy to load after that, took a lot of patience and time before he would be an ok (not good, but ok) loader... but can't say I blame him!