I have the Dillon. I debated getting the Giraud. But, for my reloading method, it was the best solution and much quicker than the Giraud or Gracey (in the bigger picture). I reload mainly precision 308 Win. (for use at a 1000 yard local range, which I am a member). I've got my entire reloading process down to two toolheads on my Dillon 550 and two tumblings. And yes, its still very accurate.
There are a few points that I had to address in order for the Dillon trimmer to be a viable solution:
1) Neck tension. The stock Dillon dies comes in at around 0.330" around the neck. I opened it up to 0.336" on a lathe, which is ideal for the Lapua brass I use. Anyone with a lathe can do this for you in about 5 min. There are also companies such as CH4D and Neil Jones Custom Products that can make you a custom trim die, with specific neck tension, that neck sizes only or even a FL dies that is tailored to your actual chamber (if you send them a fired case - Neil Jones only). CH4D only charges about $15 more than Dillon for their custom die. The neck tension issue can also be solved by choosing thinner brass (Winchester) and/or neck turning.
2) Chamfering the inside or the neck (outside isn't necessary). The Dillon doesn't leave a burr per say. But the edge of the cut is a sharp 90 degrees. There are two ways of addressing this: the first is to just chamfer afterwards. This isn't any slower than the Giraud/Gracey since those require sizing and with the Dillon the trimming is done during sizing. So either method is sizing plus a case handling operation (same s**t, different pile). The second method (which I use) is to install a Lyman 'M' die in the Dillon Tool head. This makes chamfering unnecessary (with the Dillon, won't help with a manual trimmer). It expands the case mouth about 0.002" over bullet diameter, just at the tip of the case. This doesn't change neck tension over chamfering since you aren't getting any neck contact in the chamfered area anyway. You can also add a Redding taper crimp die after the bullet seater to bring the bell back in a bit. This also rounds the outside edge of the trim as an added bonus. I wet tumble with 1mm ceramic media. In addition to cleaning the insides of the case and primer pocket, this also rounds the edge of the cut slightly. Kind of makes it look like new brass.
3) Changing calibers. I put a Hornady locking ring on my trim die, which makes adjusting the size length for a proper 0.002" shoulder bump a heck of a lot easier. The Dillon nuts are only there to torture you... they're useless! I made a locking ring for the trimmer motor side of the die. Alternatively, you can use two nuts on that side and lock them together. This way, you just unscrew the motor from one die and screw it down on another. Its quite repeatable.
4) Vibration. On a Dillon toolhead, this thing rattles around like an SOB. Having worked 10 years designing automotive parts, I can tell you that movement under vibration is a bad thing. It wears down parts and worse than that... its loud and annoying as hell. The solution I found mimics this:
http://www.uniquetek.com/site/696296/product/T1230. However, I just bought the 5-40 helicoils and STI tap, shaped a screw for an insert tool and accomplished the same thing for around $10. I believe the Dillon toolhead should be free floating for normal operations. But, with the trimmer, this is a must. Not necessary if you're using it on a single stage though.
Now, let me dispel a few rumors and misconceptions about the Dillon trimmer. First off, the Dillon trimmer does trim squarely. Your case is being aligned by the die square to the cutter. Also, its does trim accurately. My results are always within +/- 0.001", consistently. Now, someone will inevitably point out that their hand trimmers will always hit the same length, right on the same 0.001" mark. This is true, but guess what? if you're chamfering with a hand tool, the depth of that chamfer isn't going to be within +/-0.001". You'd better be chamfering on a setup similar to a trimmer if you really think thats important. Using the 'M' die, the depth of my "chamfer" is very consistent. More consistent and square than something being done between one's hands, I guarantee this.
In the end, it depends on your reloading practices. I personally hate reloading... especially the tedious steps that involve handling cases. So, I've built my methodology with that in mind. The Dillon trimmer fits it very nicely. I spend a lot more time on the range than at the loading bench and I can create a ton of ammo in a very short time.
