I just bought a $359 RedMax BCZ2650S trimmer (made by or fronted by Husqvarna) a few days ago after my Tanaka 245PF crapped out after 8 seasons. Its a commercial grade trimmer, regular torque, 1.2hp unit. Redmax makes a max torque commercial unit that runs around $400-450 depending on store discounts.
Used the RedMax to tidy up about 1/4 mile of firebreak around my fencelines. Appears to work fine. I had the tech at the Ace Hardware store where I bought it remove the bump type string dispenser and replace it with a $20 no-brainer type Tanaka string holder that takes 16.5" long pieces of plastic string. I prefer this type because I hate messing around loading 20 ft of string in one of those bump types. I use that red-licorice type ribbed plastic twine (0.120" and 0.155" dia IIRC) rather than the smooth style twine since the ribbed stuff is much more durable.
I use the snot out of my string trimmers--mowing 1/2 mile of ditch and fenceline several times a year, tidying up 1/2 mile of 30-ft wide firebreak in addition to cleaning up almond orchard and the usual trimming round the lawn areas.
Good luck.