The auto-darken ones are good for hobbyist welders who only do a small amount now & then. There's a slight delay between the arc & when they darken, and after a whole day of welding, your eyes will feel like they're full of sand.
I've found for the odd jobs, auto-darken is great, but for a day of car repairs with a MIG, the old passive one is the only way to save your eyes.
It's kinda the opposite to what you're doing - the short job where a/darken will be fine, so the delay won't be an issue for you, but it's hard to justify the cost.
One thing I have learnt though, if you own a welder, and your skills are reasonable, your buddies will catch on, then you'll find yourself doing a lot more welding jobs once word gets out - which would justify the added expense.