This review covers all the basic 100 Watt MFJ tuners. The design does not change from model to model except for additions of antenna switches, baluns, and SWR meters. Even the newer offerings are the same simple T match circuit, with similar ratings. The larger 300 Watt units are generally better quality, and the biggest ones are much better. But none that I have seen approaches the quality and performance of the Dentron MT-2000A reviewed on this website, except for the most expensive offerings. The bigger new Palstar has been reviewed well in QST.
Let me make this clear at the outset: this is an ECONOMY tuner at a bargain price. It is unfair to compare it to transmatches outside its price class. This transmatch is very compact, making it ideal for portable or field day operation. It is easy to use, and even in this basic form includes end fed wire and coax feed connections. See the photos for the SWR bridge and MFJ-900 that I use for portable operation. Nice and compact. These can be had used for inexpensive prices, but take off the top cover and inspect them for damage before buying at a swapmeet.
This unit can be used for coupling a solid state exciter to an older grounded grid amplifier which does not have tuned inputs for low SWR to the exciter, such as the Heathkit Warrior or some versions of the Gonset Linears.
While it claims 160 Meter coverage, it did not handle the match needed for my full wave loop. It came close, but not quite enough. Other bands worked OK, as long as you did not exceed 100 Watts output. I only tried it on coax fed dipoles, to extend their operation to band edges, at 6:1 maximum.
One problem with the design is the compactness of the cabinet. The coil is spaced less than ¼ inch from the aluminum top and bottom panels. While this size allows easy portability, it has its down side. The smaller Ten Tec transmatch I review on this page is similar in ratings and features, but it has a clever variable toroid for the inductance to solve the coil problem; this makes it more efficient, but it generally costs more used than this MFJ-900.
The other serious MFJ-900 deficiency, which can be corrected, is the use of two ground lugs to mount the main coil. See the photo (red circle) to view the plastic tie wrap anchor I employed as a replacement for the ground lug farthest from the end of the coil. This increased the available inductance for 160 Meter operation. More importantly, it eliminated a shorted turn which reduced Q of the coil and increased losses in the transmatch.
The inductance switch could flash over with extreme loads and the capacitor air spacing could also give problems with high impedance of highly reactive loads from random wire end fed antennas. These are commonly reported problems on eham reviews.