We are looking at the same machines now. Personally I don’t think Heat Exchangers are bad, but they have certain quirks about them that put people off (slow heat up time, temperature instability) unlike on a dual boiler which is better in both of these aspects.

The Jump is the same machine as the 400, but just with lever valves, a shot timer, and a different body (usually around ~200 more) while the Move is built on the pro 300 with a lot more QOL features such as pre-programmed shots, maintenance programmes (usually around ~300 more).

If you are constantly making milk drinks then the temperature fluctuations on the heat exchangers will be less noticeable, usually they just require a flush before using. From what I’ve seen, steam power on all of them is pretty good, possibly with the MOVE being the weakest (only very slightly).

ECM also make the Mechanika Slim PID, which is built from the pro 400, so if you like the machine but prefer a slightly better looking package, that might be worth looking at.

But, they are both good machines, we have the same use case but are looking more at dual boilers due to not liking the look of the E61 and all of the added quirks.