The Ten Tec 291 transmatch is more efficient and better designed than the MFJ900 econotuner.
It does not suffer from the losses inherent in an air wound inductor mounted too close to the chassis with a shorted turn in the design. The inductor is a toroid that has a wiper on it like the old Variac AC Voltage transformers. So it is nearly continuous rather than switched to taps, affording a closer match.
While it is slightly larger, this is a good choice for 100 watt field day installations.
Both of these require an external balun, if you wish. I NEVER find built in baluns satisfactory and prefer to provide my own current balun, mounted at the exact optimum feedpoint location.
Neither includes a power/swr meter, but again, I prefer to provide my own external meter.
Neither is suitable for anything more than a 100 watt ssb or CW rig, regardless of advertising hype.
The Ten Tec matched my 160 meter full wave horizontal loop on Long Island easily. The MFJ did not.
Both are economical compact transmatches well worth your consideration, if you operate them within their inherent limitations.
Here is the manual. It is much more comprehensive than the MFJ 900 econotuner.