I went through this same evaluation when I bought our EVSE and the UL listing may or may not be a big deal to you depending on your city location.
Originally I ordered a Juicebox for the same reasons as above however when I found out it was not UL approved, I had to return it. The City of Los Angeles requires that it be UL approved and you have to get a building permit and LA-DWP inspection. Since adding the EVSE (of any brand) was going to be a very big expense for us (meter upgrade to 200As, meter relocation, pull back three conduits for the three circuit breaker boxes located throughout the house, installing a ground wire across the house, and add the EVSE circuit also across the house), I wasn't going to take the chance that they would not sign off on the inspection because of that requirement.
We ended up buying the Leviton box which is also rated for continuous 40A charging (50A circuit) and is UL approved. Since neither our B-Class or the Leviton box have builtin timers, I just had an Intermatic mechanical timer (40A) installed ahead of the Leviton box. It works great and I don't have to worry about websites or WiFi connections. The only maintenance is just to reset the clock after a power outage (not a big deal where we live).
Our box would also be considered a "portable" since it has a plug in cord similar to the Juicebox but it is really just a relocatable box (a box that you can take with yo if you move). I would not take it on the road with me anymore than I would a Juicebox.
For a truly portable, I'd look at the JESLA cord set which is basically a Tesla charger re-worked for J1772 vehicles and supports connectors for any normal electrical connection.