I'm happy with the results I get using software,
Those Lee graduated filters are an awful lot of money for something that I'd only use occasionally.
I can't justify £100+ for a filter and £50+ for the holder, plus it's yet another thing to carry, keep clean, and risk getting broken.
I've already got Lightroom so why not use it? If that isn't enough I have a Topaz plug-in that does a pretty good job.
It strikes me that anything that does "not darken unwanted areas." isn't going to be very effective at darkening the areas you want it to.
The amount of unwanted darkening is going to depend on the size and shape of the intrusion across the dividing line, and that's something you can never predict.
When questioned, one of the guys at our club who uses grads said "sometimes you have to selectively brighten the areas you didn't want to darken" in which case why not do the whole thing in software?