Magna:
It depend on the stock you trade. Typically I find thinner stocks to trend a lot more smoothly than liquid ones. Any size in a stock like GE or IBM probably doesn't matter, but in a stock like AGN it can be vital. Also first and last hour of the day I typically don't see much fake sizes. Yeah, there are traps, like a stock goes up a little then tanks, but the sizes are usually real.
I also don't mean buy just because there is a BID, with the exception of a stock that just opened, I would typically want to see some sort of a BID before I jump in, no 2x10's. Something like 30x10 is enough for me, in other word, wait a little until the tape confirms.
Def:
I am not saying you can't make money going natural, I am saying bullets are far, far, far superior in stocks that trade under a million shares a day. There are some serious advantages of trading thinner stocks (cleaner tape, easier specialist, BID/ASK usually mean something), and even in more liquid stocks, sometimes the bullet is the only way in.
I always scale into the position, and without bullets, it is not possible. I don't hold stuff for multiple points, just one momentum move is all I look for, so the style is different as well.
I didn't feel bullets are a huge advantage either, but back in March there was a day market tanked off the open, and I splitted a few bullets with a fellow trader to save on cost, it changed the way I look at bullets forever.
I trade via tape, and if you can get a natural filled, chances are, the stock will usually move up a little more before/if it tanks, you need to give at least an extra 10 cents wiggle room to natural shorts, on 1500 shares that alone is $150, and that's the cost of two 1500 shares bullet, not to mention you usually have to get your full position in one shot when the tape is moving against you (otherwise you won't get the uptick fill). My max size is 1500 shares I already see a big disadvantage, if you do bigger sizes, bullet is not an alternative, it is a standard. If a stock filles 3000 shares on a natural, you don't want to short it.
Yeah, occassionly I still take natural shorts, but for all of my serious positions, it is either long or bullet short . . .