The other is a propellant-less thruster that has experimental evidence backing it up AND could potentially one day lead to 35-day Earth-Jupiter transit times.
Am I hearing that right? 35 days from Jupiter to Earth? Fudging the numbers gives me... 926841 km an hour. Of course It can be more/less then that depending on the two planets orbits, but damn...
You're thinking about it like it's on Earth (e.g. in an atmosphere); in a vacuum, the only speed limit is light, all other speeds are arbitrary (just depending on your chosen reference frame). What is more important is the rate of acceleration, as basically it just accelerates full tilt to the half way point, flips around, and starts deaccelerating.
What if we add more power? I mean, is it even remotely feasible to get to Andromeda or Alpha Centauri within a human lifetime? What happens when we stop measuring power output in Megawatts and instead go to Gigawatts? Terawatts? Exawatts? What would we even need to make that leap in power output?
It's an exciting time to be studying SciFi (yes, I have a real college course in SciFi. I'll be bringing this topic up tomorrow.)
Basically, our frail human bodies are limited to maybe only 2G's (I'm spitballing, I would appreciate any real studies) of sustained acceleration, tops. That means Andromeda is a biiiiig nope.
Alpha Centauri is possible, if you don't mind waiting a number of decades though; of course, it already was with Project Orion style propulsion (IIRC 70 years was the rough estimate given, using 1950's tech).
Also be sure to actually print off the article; it's pretty out there sounding stuff, so it's handy to be able to point to a source.
Also, remember, this is a PROPELLANT-less drive (much as a light sail would be), not a reactionless one (that's impossible).