Had the opportunity to ride the TerraTrike Rambler EVO for about 7 miles, so thought I would put my impressions out there.  We had a Rambler for about a year (2013?), and really did not like it - the relatively high seating position combined with direct steer made it very twitchy, and tippy in turns...  Dave Rothgeb tipped it over turning into a sloped driveway, once, although I never did.  So, I didn't think the EVO would necessarily be much of an improvement... but wanted to try out the Bosch e-assist, anyway.
 
First off, the Bosch -- putting it on the Rambler increases the price by about $2,200 from a non-assist model.  However, it is a VERY nice e-assist -- smooth, quiet, responsive, and powerful.  They mount the front motor on a special boom, as opposed to just installing it on a typical bottom bracket, and the battery is mounted low in back on a tray.  I didn't really ride it far enough or hard enough to get a feel for battery life, but it's probably fairly standard, perhaps 40+ in ECO mode.  There are four assists, ECO, STD, SPORT, and TURBO, and assist speed is regulated to 20mph top.  I would think most "beginner" riders would use STD mode.  I'm not sure how the Bosch can be adapted to other brand trikes, but its definitely an e-assist worth looking into.
 
Regarding the Rambler itself, it's basically unchanged - although this model had trigger shifter for the rear cassette, which worked just fine...  A point in the Rambler's favor is that, having the motor and battery mounted low actually improves the stability of the machine, especially in turns, which was a pleasant surprise.  However, in my humble opinion, you still don't want to take a Rambler much over 15 mph -- so the assist can get you quickly up above speeds you might consider safe.  It's still a fairly twitchy machine, with the direct steering, and you can make a pretty sharp turn compared to an indirect steering machine.  In higher assist modes, just a light pedal pressure at 70-80 rpm, and you're zooming...
 
The other somewhat negative aspect to the Rambler is the "straight out" boom - there is no incline raising the pedal position, so you can get occasional heelstrike with the GROUND, depending upon your shoe size.  Having shorter cranks can help alleviate this. However, that straight out low pedaling position also can result in the front edge of the seatmesh hitting the backs of your thighs, which could be an irritation on longer rides.
 
If someone is considering a "starter" trike and needs e-assist, this isn't a bad choice, although the >$4K price tag puts you into the range where there are potentially better machines out there...  putting a Bafang on a Cat Villager will take you up to $5K, by comparison.  The Rambler EVO is worth a test ride, and the Bosch assist is great.
 
Enjoy,
Paul