Re: I’m interested in hearing form drummers who have study Benny Greb’s letter system
Benny Greb's system is very similar to how I developed rhythmic layering exercises for myself as was first learning to play, so the whole thing felt very natural when I started working through his DVD.
First off, the ability to play any possible rhythmic variation in a given subdivision of the beat will do loads for your confidence insofar as you'll never have to worry about losing your coordination (re: independence). If you take the time to work through accents, doubles, buzzes, flams or any of the possible stroke combinations not included in his DVD, your level of execution will rise to effortless, depending on what tempo/subdivision your working towards and how hard you plough through it all. Layering this through all four limbs against any ostinato you can come up with basically solves every coordination problem your typical drummer encounters.
I took the New Breed route with exercises like this - using two or three of the patterns stacked on each other as an ostinato, then reading through all of the rhythms (or "letters") with a seperate limb. You can get very heavy with stuff like this - as deep as you have time to commit. Imagine playing a sequence of M-N-O-F with your RH on the ride, I-C-N-M with your RF, upbeat 16ths with the LF and then soloing through the letter chart with your left hand on the snare and toms. You can do this forever, making new combinations - but thankfully it's not very long before you have some serious independence, and you don't have to try anywhere near the possible variations to feel in complete control of your drumset (think "headroom" - you'll have lot's of it!).
So you ask if I feel that it improved my timing or independence - I'd say Benny's system (or should I say a near-identical process I worked myself through) helped me to master practical independence, and has allowed me to keep perfect time no matter how complex the pattern I'm playing may be. After working out all those subdivisions and combinations you can really relax in the moment and focus on groove, dynamics, and the full-band sound.
And I've practiced these ideas both ways, with a metronome and without. Early on, the metronome was essential to feeling these patterns in good time. Later on, as my internal sense of time (and more importantly, groove) started to strengthen, practicing without the click became an important meditation. I also appreciate Benny's exercises on bringing the click in and out during a groove. Once you have things like that down, you stop worrying about time and you just feel the groove - it's very liberating!
Edit - PS. Here's a tip not included in the DVD that I like to do with his system - specifically for fills. You can use each variation as an exercise in hand-foot fill-ins, for example doing M (o - o o) as snare-kick-snare-snare. Or try doubling the notes to 32ns, so T (o o - ) would be snare-snare-snare-snare-kick-kick. You can get a lot of classic fills out this way, and once you start combining letters into phrases (M-G-J-N) you can develop some great, longer-phrase ideas. Those are just 2 examples, but there's so much more you can do with an open-ended system like Benny's.