This is seemingly an old thread, but I'll add my two cents.
Having owned and used the inflators that deflate all four tires at once, since I was accused above of not having used that style or I wouldn't have been against it, I'll just say again how I'll never use that style again. The problem is they are slow because they don't remove the tire valve stem. The cheap deflators don't and that's why they're so slow. Many don't care if they are slow but in advanced offroading groups, few use slow deflators and those using slow deflators soon start noticing everyone else is ready to go and waiting on them to finish. When we are in a rush to get going like due to other groups waiting behind us, those of us with fast deflators like Currie's and ARB's will take them over to help finish getting people aired down. Plus those deflators that don't shut off automatically can air a tire down too low if you spend too much time at a tire or two trying to get the pressure where you want it. I've seen that happen, where the driver would have to get his compressor out to raise the pressure back up. Then there are those who don't want to be 'hunched over a tire' with the ARB/Currie style deflator That's fine but I'll be done airing all of my tires down in 5 minutes total and out helping others get their tires aired down well after I'm ready to go. The more people wheel, the more they are looking for something besides cheap deflators that are slow. The newer they are to offroading or the less they go offroading, the less they believe they need anything more than the cheapest deflators they can find. If you become a regular active offroader, it won't be long before the cheap deflators begin showing why few long-term experienced offroaders use them. And for those using automatic offroaders, I personally don't believe there is one magic air pressure that is good for various trails and difficulties. The only way I'd run an automatic deflator again, which is one of the styles I owned and used for a year or two many years ago, is if I confined my TJ to the same trails and wasn't doing different levels of trails. I run my tire pressure anywhere between 4 and 12, there's no single air pressure that would work for me.
All the best,Hauvet