I have a couple different sluices and I use them regularly. I've found more gold with a sluice than any other method so far. I usually sample pan until I find a good enough spot to set up a sluice.
I was born and lived in sturgis, south dakota and I explored and hunted throughout the black hills ever chance I got. I got gold fever when I was 13 watching some older guys sluicing and panning. They told and showed me where the gold likes to hide along the creek. Some creeks in the area seemed to have gold everywhere. Sample pans in some spots showed 2 or 3 specks while other spots the pans would show 10 to 20 specks along with an 1/8" flake or two. Those spots were where those guys would set up their classifying screens and sluices. I learned then to not just set up anywhere. Sampling different spots I have found is always a good idea. Why would you want to just look at a spot and say " this looks good" and shovel all day for just a few specks in your pan? I wouldn't and don't. I want to get the most gold for all that hard work I do.
Can't say for Montana but the creeks I had the best luck at in South Dakota had hematite in them because it's heavy. Usually the more hematite pieces I found in my sluice or pan mean't more gold. Same with sizes of hematite. Bigger ones I usually found bigger gold. I only found this to be true in the northern hills. I found gold in the central and southern hills but it was for the most part small specks..almost like it had been ground up. I'm just taking in the streambeds. River/creek gravels higher up away from the current stream and also cracks and crevices in bedrock had all different sizes of gold.
Long winded reply...sorry... but I would say learn what you can of the area you want to prospect and sample,sample sample. If your good at panning you can run through a sample pan in a couple three minutes...doesn't take long and it pays off at the end of the day.
Since you grew up here maybe you could show me a few places where we can fill our pans with some of that yellow metal. I've been prospecting for a long time and was south dakota state director for the gpaa for 10 years and would be willing to help you anytime.....just holler. Good luck!