Here goes nothing.
Yes, all horses can go barefoot. Yes, some climates are easier than others. Yes, sometimes it just takes time to adjust.
HOWEVER sometimes it is better to take the route that some here have chosen and just stick with shoes. Those cases where the horse is so uncomfortable that it would mean laying them up for more than a year and the use of boots at all times until the horse is more tolerant of being barefoot make barefoot impractical. Wet conditions are very difficult to maintain hooves in.
For the question of what kind of trimmer to use. Drumroll please... A farrier who actually balances the foot correctly does so in a trim or shoeing. Unfortunately, it is easy for someone to put out a shingle saying they are a farrier and have no clue about what they are doing. I use a regular farrier to do my horses' feet who are barefoot and have 0 problems because he is knowledgeable and capable. I have had barefoot trimmers who never took the time to actually learn about their trade who have crippled horses. It goes both ways - the key is if it's working, it's working, if it's not, it's not.
As far as length of time between trims - I have several horses that are NEVER trimmed (going on 5 years for the one) - they live out in a pasture that has grass, dirt, rocks, mud, and wetlands, and they move around enough that they don't need to be trimmed. I have another horse who HAS to be trimmed every 3-4 weeks no matter what kind of terrain I ride her on. I have a few others that can go 2.5-3 months between trims. And then there's my broodmare that has 4 shoes. They all have gorgeous, balanced feet. Every horse is unique, every horse has its own tolerances.
Boots can change the way the horse moves and stress joints and muscles, we have a horse here that when he throws a shoe we can't even put an easy boot on because he interfers and has to change how he moves which then creates problems in his shoulders or stifles (depending on whether it's front or back).
As to the actual question - we've had success with the Old Mac G2's - I recommend using the socks under the boots - but they are pretty clunky for a horse that is a more delicate structure or moves closely with its legs.