So please tell me why you cleaned your masonary chimney more then the steel one.
Because I didn't install it and never knew for certain if it was entirely up to snuff and never wanted to test the limits. Fewer masonry chimneys from the 70's and 80's were properly built as folks would like to think, so erring on the side of extra caution with them is simply wise.
As it turned out, it's a good thing I kept up with / did more than necessary with the maintenance and never tested things out. A few years ago I found the thimble was incorrectly built and was way too close to combustibles. One chimney fire in that thing might have been one too many.
As it was I never got much out of the monthly cleanings but with an exterior masonry chimney it potentially could accumulate more creosote than a stove operated the same but connected to an interior chimney.
With a rebuilt thimble that meets clearances, and a liner that has insulation, I have a pretty high level of margin in the event the wife or I accidentally turn the stove into a light bulb and burn whatever little creosote there is in the chimney. Even going 2 or 3 months between cleanings now, I still don't get much more than peace of mind and hope it stays that way.
For what I do get, there's no reason I couldn't extend the cleanings out to once per season or once per year even. But, if it's easy, it just doesn't make sense to me to not go the extra mile.
Each and everyone is free to do what makes them sleep best at night.
I hope the original poster now has a plan that he's comfortable with.
pen