My daily helmet is an old Miller Elite XLsi that is now obsolete. It's a great helmet, but the lens got damaged and a replacement is around $250. To get by, I bought a Northern Tool unit and swapped the lens out. It fit in the Miller well and the external adjustment dropped right in, even using the Miller knob.
I liked the fact that it was auto on, and it works great for bench work and MIG, but it absolutely ***** for out-of-position TIG welding. It will shut off if you are not directly looking at the arc. Even if you have a clear view and the sensors are unobstructed, you must be looking straight at the arc. I was trying to TIG some fuel line bulkhead tabs on the frame of a '72 Bronco the other day, and it was so bad, I stopped and picked up a HF helmet for $35. It did the same thing. I had to tuen the sensitivity up, aim my drop light at the lens to darken it, and finish the work.
If you can afford it, pick up a Miller, SpeedGlas, Jackson or Optrel helmet. If you can, try one on before buying. The headgear is an important part of the helmet. The cheap units have the worst headgear. They are uncomfortable, and have no cant adjustment which is important when welding out of position.
If you can't afford a good auto darkening helmet, pick up a Huntsman with a large gold lens and use it until you can afford a higher end helmet.