I have a Cub I built for 40M. It works pretty well and there are some modes for improvements. Mine put out 2 watts and was best used on my home antenna system; though, I did make contacts with some wires and Emtech tuner.
I have one each MFJ 9020 and 9040. I have had a lot of fun with these little rigs. Both were bought used. The 40 meter one drifted but I knew it before I bought it. That was an easy fix. I just changed two of the caps in the VFO circuit. MFJ sent me them both for free. Even when it drifted all I had to do is let the rig on for about 30 minutes and it would settle down.
I'd get another one in a heart beat.
I still have both of them and use them but bought the Ten Tec R2040 CW QRP rig. Good buy for the money, only $249.
I have a few of the 90XX series. I didn't have a drift problem in any of them, maybe I'm just lucky. I did have low audio (found a fix in QRP Quarterly) and used a different series lm386. The volume controls went bad in a couple, and one had a "lumpy" feeling tuning cap. Guess the ball bearings made indentations in the mating parts. I exercised it with 3in1 oil and a small reversable drill until it moved smoothly. The accessory keyer and audio filters are clever, but it gets annoying to reach behind the unit to make adjustments. All in all, I'd give 'em a B+.
I had a 9420 for several years. It was a great radio. Good audio both ways. The only thing that ever was wrong was the transmit led would not come on. I found a missing 2.2k resistor. I installed one and the led worked fine. I sat on Kualoa Beach on Oahu and worked the USS Missouri on the other side of the island and mainland contacts all the way east to Boston. It was alot of fun. I sold it only to upgrade to a multiband radio. Geoff, AJ8L.