We have owned 3 Motor Homes with single axles and bought the 45 Monaco Signature with tag axle 2 years ago.
We took a trip on New Years Eve 2015 from Oklahoma to Long Beach, CA. We were also pulling a 37ft Boat trailer about 8750lbs. We hit a big snow storm just out side of Flagstaff and had really bad road conditions all the way to Kingman, AZ. The tag axle was worth its weight in GOLD. It kept us stable and on the road down Ash Fork at 6% grades. Many cars and trucks were off in the ditch. We stopped in Kingman because the closed down I-40. When starting back we began to spin the drive axle wheels at start up roll. We just hit the tag axle air retract and got it moving and dropped the tag back down. It was awesome! It has made us a believer and will not buy anything without a tag in the future. Fantastic ride and worth every penny of any extra expense.
http://www.liquidmarine.us/rvboat.jpg