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The Ktrak kit consists of (2) Quick-Release replacements, a ski that replaces the front wheel, and a complete track assembly that replaces the rear wheel. The rear track also has a shock absorber assembly that clamps to the seatpost, and keeps the track's three smaller wheels in the correct position. The manufacturer says it can be used on both Sand and Snow.
The EcoSpeed is a mid-drive kit using a geared BMC motor to drive a proprietary chainring, and power the bike through the gears.
Someone here recently posted about the K-Trak, with picture I thought unusual enough to research. It looked fairly practical in the pictures, but elicited common complaints about the track adding too much weight, and being too hard to pedal. The rolling resistance of the rear track, and friction surface of the front ski, make the folks in the youtube video look like they are struggling when not going downhill. I'd expect everyone on this board is scratching their chin at this point, and thinking "so obviously, all it needs is a motor." Well, there was a guy who put a gas motor on one, but its youtube vids looked like it would benefit more from the linear control and clean running of electric. There also was a for-sale posting from someone in Canada with a ford think electric bike with a ktrak, so it has been done albiet not documented... finally the ktrack was far enough off the beaten path to catch my interest as a potential project.
They haven't been made for years, but I found a ktrack on ebay for far less than I expected, so I idly posted the only bid and eventually won it, sort of accidentally committing myself to a project. Years ago I had purchased some sort of mid-drive kit from Cycle 9's clearance sale, but the kit wasn't complete as Cycle 9 advertised, and disappointed I never got around to researching the missing parts... Now, powering the Ktrak gave me a reason to revisit it. I also needed a donor bike, and I chose one of my old reliable mules, a Tidalforce S-750 that has been at least (6) completely different eBike drivetrain/controller/battery/fork configurations, from a 5305 NiMh wheelie special in 2007 to a Kepler friction drive.
I was pleased to (re?)discover my midrive was an older version of the quality Ecospeed kit I have seen pop up on numerous builds. The supplied aluminum clamps were made for round tubes and not going to work with the sharply oval TF downtube, but I saw a picture using pipe clamps on their website, and decided to go that route. The bottom bracket was missing from the kit, and it looked like the taller stack on the Ecospeed chainring was not going to clear, so I contacted Ecospeed for advice. Tad was really helpful, and offered me the 27.5mm bottom bracket I needed for $19. I have one of the oldest kits, which has a mounting ring that clamps between the right side bottom bracket and the frame. Tad also recommended a retrofit kit that adds a second mounting ring between the left side bottom bracket cup and the frame; I had already half-way engineereed a similar solution in my head, but I was glad to buy the precision fit and time savings of a proven kit instead. It turned out that the left bracket kit also required that I replace the Primary and Secondary plates (tertiary is the red plate the motor is bolted directly to). The new plates are also designed to accomodate a pipe-clamp for the downtube mount, and I think smaller/lighter than the my old ones. The left-bracket retrofit also takes a lot of load off the pipe clamp, and stops the "eventual rightward creep" of the first generation kit.
It didn't jump out at me at first, but I've really come to like the space where EcoSpeed put the motor. It is otherwise dead space, and obviously carrying the mass forward and low enhances stability, but it also puts the motor chainline as far from the rider (and pantlegs) as it can get. I ride street so I don't have to worry about mud kicking up from the front wheel into the motor, or I'd make some kind of shield. Still, I plan to make an interpretation of the chain cover available on their current models, after I sort out an idler arm.
Short term, I'll throw some a123 20ah packs into my old ammo-can front mount. Long term, I am thinking of spot-welding a bunch of old Dr Bass 1.1ah a123 cells into a pack shaped to fit the triangle. I need to get a sense of what voltage/RPM I want to the kit at, which will dictate how I serial/parallel the qty of cells that fit in the triangle. My kit came with a BMC 36v controller, not EcoSpeed's new snazzy controller; I'll see how the BMC runs, maybe swap in a few other controllers from my vast collection, in pursuit of optimal voltage for my preferences. BTW does anyone know if this 36v nominal BMC controller can handle up to 50v like the 36v xlytes did?
The Ktrack is a well engineered piece of kit, and it bolted on as simply as any other quick-release wheel. A seatpost clamp and shock absorber keep the trailing wheel assembly in position, and is as easy as adjusting a seatpost. The front ski looks sturdy, but it is meant for a QR fork not a 20mm through-axle boxxer. Ktrak said this kit was made for sand or snow, here in LA the sand is much closer, so I'll probably try the surfline with the track and front wheel first, and swap in QR fork when I plan to try snow. I'll probably run this bike with a regular rear wheel far more often than the ktrak, but it was the motivation to do something with the EcoSpeed, and so simple/fast to install that I can convert to it in a few minutes.
I had finally made up my mind to go with an eZee kit for mine as my first build after debating DD vs geared hub vs mid-drive in my head for months. Now I'm debating again. 
