I agree the problems can be totally avoided by incident metering with a touch of judicious spotmetering.
I don't have a Zone VI modified meter, but I think it is worth estimating the problems the modifications tried to resolve. If I find the problems only cause one stop of issue, I'm probably going to drop it in with other "one stop" issues that tend to cancel each other out.
The article about meter modification in Zone VI Newsletter Number 37 was written by Paul Horowitz. I have to admit I like Paul's style more than Fred Picker's. He seems impartial and scientific, yet he writes clearly. (Paul gave us the stabilized cold light head. I wish I had one, I undestand those live up to the advertising claims).
Paul introduces the problem clearly... "Objects placed on Zone V sometimes wound up on the print as Zone III, sometimes Zone VII. There seemed to be some persistent errors -- foliage always underexposed from one to three zones, sky consistently overexposed, typically a stop or more. Late afternoon often seemed to produce underexposure. And shadow areas that metered as Zone II often "dumped" into total black."
My Sekonic L758-DR is sensitive to infrared. I get EV 12 when I meter the illuminating LED on the ATN-Viper. This is near infrared, but I've tested that it doesn't significantly fog TMY-2 in 15 minutes.
Foliage is an interesting problem. It's green, but reflects infrared. I hunted the backyard with my first-generation infrared viewing scope looking for illogical examples. Maybe because it's late summer, I didn't find any extremes (except a red apple looked light).
I tried to find infrared by metering first with my spotmeter (responds to infrared) then with the SEI photometer (it shouldn't respond to infrared - it uses my eye as a sensor). As Leigh points out, the angle of measurement can affect readings and natural subjects are inconsistent. I didn't find any significant departures. Sometimes I'd find one stop difference but other times I'd meter the same.
Then I got to thinking... What do photographers sometimes do when they want to darken leaves? A red filter of course... What does a red filter do to the infrared. Trick question - it does nothing. What does it do to the visual image of a green leaf? It darkens it.
This is where I think meters do poorly - through red filters looking at foliage!
I aimed the Sekonic at a gray target and metered with and without the red filter. Three stops difference. I aimed the Sekonic at a dark green leaf with and without the red filter. Two stops difference.
If I meter foliage through the red filter, the recommended exposure will be off by one stop. It will be underexposed.
Now the fun begins. Meter places the leaf on Zone V but I previsualize a bit darker, so I place it on Zone IV. But due to the error it falls on the print at Zone III.