The "bit of practice" I refer to has two aspects: 1 Diving exhale feels totally different from full lung diving, it takes time to figure out what it should feel like. At first, exhales near full can be dangerous, as mentioned above, especially full forced exhales with reverse packing. Further, depth range is constrained and you can get squeezed easy(personal experience), even in the pool. Warning signs are easy to miss. 2. The body makes physiological changes when subjected to exhale diving. It takes a lot of time to adjust and get the full benefit of exhale.
The key is practice a lot and explore the technique, work into it slow. "real" deep dives are unnecessary and probably counter productive if done too soon. IMHO, as a style of diving, exhale is best suited to relaxed recreational diving in medium depth. Its the ultimate "lazy man's" style. Depth comes, but its not the main point.
I found pool work, 2-3 days a week,to be very effective in building exhale diving capacity, as described in the referenced thread. Note the time scale of thread posts, it takes a while. Real diving is much faster.
Something I'm experimenting with. Try a series, 6 or 7, short(40-60 seconds?) dry statics with full, forced(but not extreme) exhale. Hold to the first contraction, until it gets uncomfortable but not much past(remember, this is the lazy man's way). What do your legs feel like? You should feel blood shift, blood leaving the legs on hold and partially coming back when breathing starts. How early in the hold does the feeling start? You should find that blood shift is cumulative, getting stronger over the series of holds.
This is a great way to shorten your warmup time when you get to the pool or in real diving. I think (could be wrong) that it also helps train dive reflex to come on faster and stronger. If you try it, let me know how it worked for you.