Were those that dry hatching hatching Guinea eggs, or any other thick shelled eggs? Chicken eggs are super thin shelled compared to Guinea eggs... plus Guinea eggs take 26-28 days so they are in for a week longer losing more moisture from the eggs than chicken eggs do. Plus the thin shells are easier to hatch out of. Guineas really have to work for it, big time. I'm interested to know if it works or not, but like I said, I don't want to risk my keets, lol.
Humidity is low here too, my airtight woodstove dries out the house in the winter (but maintains around 22% RH), then I'm dealing central A/C in the summers (it's usually down around 11% in the summers)... I only have to fill the middle trough/reservoir in the 1588 tho, and it holds 46-48%. I have to add water every 4 days, usually when I see it drop to the high 30s. I don't hatch in mine, but if you need extra humidity besides adding water to the other reservoir, there's lots of tricks.
The Accurites are good hygrometers, most are thin enough to just lay flat in top of the eggs, and not worry about messing with the sensors, but that's your call. The less crap getting knocked over on top of my 'bator and scratchin' the window, the better IMO, lol. You can check the RH calibration on it with the salt test, just to see how accurate it is, (it may be off a small % either direction). With Guinea eggs the RH is a little forgiving tho, if it's a little too high or low you are usually still ok... so just in a general range is fine (40-50% for incubation, 70-80% for hatching). Can't say if that's the case for chicken eggs tho.
I am absolutely not a fan of still air incubation. I have nothing good/nice to say about it, lol. The 1588s are a piece of cake, you'll do fine this time, so you can relax. The preset temp is reliable and stays stable. Just set it up in a draft free area and where it doesn't get direct sunlight, in a room that has a somewhat stable temp 24/7, add water and eggs and you're good to go. both of mine maintain a stable temp even if the room temps swing 15 degrees in either direction (oops, but I try to prevent that). I'd say fertility rates and egg viability will be more of a concern than the 1588 is gonna be for you.