I've seen,handled and fired several of these cutoffs, up to a 10 ga Testosterone Special H&R and the older Winchester 37s. Some were truck guns, others survivalist backups, or woods roaming guns. Some were actually delightful projects, featuring hollowed out stocks storing survival gear, jug chokes, camo paint, flares, and so on.
Some drawbacks to an otherwise excellent idea....
Light weight. The singles run way less than the Rule of 96 to begin with. Extra kick is not the only facet of the downside, the balance becomes very muzzle light,and keeping the swing going on a moving target gets really difficult. Training can overcome that, but shooting lots of shells through a 5 1/2 lb shotgun builds a killer flinch. Been there...
Also, most of us NEVER train for HD scenarios in low light. ANY shotgun with a minimum length tube has beaucoup blastnflash. Don't believe me? Try a drill or two at night.
Also, while a straight cylinder bore works for HD, keeping the choke makes sense for a GP shotgun. Sawn bbls usually have ragged patterns, even a factory Cyl bore has a couple of points of constriction to round out the pattern.I wouldn't cut a bbl unless I had the time,techniques and tools to do a good recrown...