I'm not a welder by trade, and really don't have much personal experience to draw on either. I sell parts, tools, and equipment for a living ... so many of my beliefs and opinions are learned through "osmosis". I have the manufacturer's propaganda on one side, and customer complaints, comment, and "brand affiliation" on the other.
My experience has been that you usually do "get what you pay for" when it comes to these items.
Ambient light will most certainly have an effect, and should be somewhat "tuneable" with a sensitivity adjustment.
Sensitivity is one consideration, but perhaps response time is another, more important, measure. Guys that used both a "cheap" helmet and a "quality" one will tell you about "welding flash" ... and having "itchy / scratchy" eyes when they use one with a low response time.
I have been told that the best test of response is to "flick your bic" cigarette lighter in front of it. If the shade doesn't react to that, you'll be exposing your retinas to all of that UV radiation for nanoseconds everytime you strike an arc.