I can't speak for the 300's but we have several(15 or so) Ideal Arc TM500's that have been in service for 15 years or so and are used everyday. We replaced a fan motor the other day, but no major problems. We also have a few 600's AC/DC's still no problems out of any of those machines. Seem to be very sturdy, we have even gouged on the 600's.
John Wright

I used them (250/250 and 300/300) in the mid 80s and liked them alot. Nice smooth tail off with the foot pedal. We used them for Mil Spec 1595 recertification coupons in all material groups with no machine related difficulties.

The old tall ones (circa pre 1980) were the best. I have one from 1977 and it still works great.