To summarise, a bit of personal experience.
I'm on my fourth or fifth impact - all trade use. First one was a single speed 12 volt Makita back in the days on NiCd batteries, I've had a few upgrades and I'm now on my second multispeed Makita (a DTD170). Unless you go for a 3-speed or multi-speed impact the torque generated will simply destroy small screws, such as the #6 stainless jobbies used on kickplates, fingerplates, etc. A 3-speed set on the slowest setting will handle those with ease, and without stripping/rounding out - providing you learn to feather the switch. Sorry, but a single-speeder can't achieve this no matter how much you try to feather the switch - if you need to do that a drill is far better. Impact drivers will also shear off the heads of screws when driving into hardwoods such as oak or when fixing through steel plates, etc into timber unless you are very, very careful. It takes some time to master how to do this. Drilling with an impact: the hammer action on an impact cannot be turned off, so forget that - the impact action will eventually twist smaller bits inserted into an impact, a fact of life, so whilst they can be used for pilot drilling the drill bitsm (which, incidentally, are considerably more expensive that brad point twist bits or engineer's twist bits) won't have a long life. A lot of the bits made for impact drills use a steel hex section which is crimped onto a conventional plain shank drill bit - and you can imagine how long they last before the crimp starts to fail - the only solution I've found is to use those Trend Snappy bit holders where a conventional drill bit is held in a sprung holder. The one piece forged steel bits, surely a solution, are hideously expensive and equally prone to premature breakages. Hex drive auger bits work, but the cutting edges take a beating (so need sharpening more often) and above 16mm or so they have a tendency for the shaks to twist and break. The bigger they are, the faster they'll break. It really only leaves speed (flat) bits - and they do seem to survive pretty well on impact drivers (I use Irwins)
All the foregoing means that, as most pro tradesmen know, the impact driver is a spcialist bit of kit ideally suited to driving copious quantities of largr screws very quickly - but not much use otherwise, and certainly not the most useful drill for a DIYer or handyman
