Barney,
While an antenna analyzer or SWR meter make it much easier, the SET meter on the 857D will work. As you say, make the initial tests at lowest power setting of 5 watts. If you are going to be operating mostly SSB, you will need to shorten the main radiator by a substantial amount. If you operate mostly CW you will only need to shorten it a small amount. It will come out of the box tuned right at our just below the bottom end of the bands. It is manufactured so it can be used on MARS/RACES and Civil Air Patrol frequencies as well as Amateur frequencies. The trimming/tuning procedures are well covered in the manual that can be downloaded from the LnR web site.
73,
QRPME