Years ago I purchased a Gossen LunaLux (for supposed low light performance), but I never bothered to use the incident metering. Now that I'm getting into 4x5, I'd really like to learn to shoot from incident metering for practice and expansion of my horizons.

The issue with the LunaLux is that the ping-pong-ball equivalent on its edge is rather blemished:

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I'm not sure whether it would give accurate readings. Can I replace that attachment?

I've looked around online and found that there seem to be a lot of LunaPro's and Luxes around that can be had for sub 50$ (in my interest, as I am rather low budget). However, I'd like to know what you guys think of electronic meters. It seems there is a tremendous selection of electronic meters now, with fancier incident bulb-things. Is it worth it to go up to 100$ or more for a more modern incident meter? If I'm on such a tight budget, what are my options as far as solid incident meters?

Additionally, I'd like to ask how to use incident metering. I understand it as a principle, but I don't understand how I factor that information into my photography. The only way I've known to take pictures prior has been through a rough approximation of the zone system, facilitated by a spot meter. How do I anticipate where the highlights will be? Does it give a closer depiction to the shades as they appear to the naked eye?