For those who don't know me, I've been around for years... I used to be a bit more active several years ago. Big fan of the platform/project. I started using PA on an 8GB Corsair Readout — flash drive that showed you the MB remaining right on the drive. It was really cool. Since then I've used it on big external hard drives, portable (bus powered) hard drives, USB 2.0 flash drives, USB 3.0 flash drives, and now I'm using it on a Samsung T3 portable SSD.
Oh man, this thing is fast! Platform opens instantly, and loads the apps/menu in a couple seconds. VLC Portable, which is slow for everybody, opens in about 8-10 seconds. A huge improvement over a fast flash drive or even a portable hard drive. Transfers to it are super fast, too. If you can get your hands on one, you absolutely should. The 250GB is pretty affordable at around $100 — obviously, if space is an issue, you can get a 4TB WD MyPassport for around $150 and carry all the things, and it'll be fast enough, but for the raw speed of an SSD, you'll be left behind. I had some Best Buy credit sitting around, so I was actually able to get the 500GB SSD for a fair price. It's not NVMe, but the speed at which you launch applications would be negligible at best. If you're going NVMe, you better get that in your boot drive and be running games or video editing or something equally demanding where even an SSD can be the speed bottleneck. I don't think NVMe is even offered on portable SSDs (unless you count iPhones, they use NVMe) but if it were, it would double the cost or halve the capacity. I put a 1TB SSD in my desktop computer, and I didn't go with NVMe this time. The drive was about $300. That much gets you about 500GB of NVMe SSD; a 1TB SSD with NVMe would have been at least $600-750. Tempting tempting, but a little out of my price range — and six to eight weeks back ordered.
I've heard tell of drives that are "too fast." Microsoft tried to peddle this BS when the Xbox 360 started taking external drives. If the drive was faster or equal to the speed of the internal drive, Microsoft said the drive was "probably incompatible" or some FUD like that, but it worked anyway. I remember a YouTube video testing it, installing a game to a portable hard drive with 7200RPMs, and after the warning, it was faster than installing the game to the internal hard drive. And the load times were less. So, best I can tell, there is no such thing as a drive that is "too fast" for your task. At least in the case of portable app drives. Go ahead and throw the Platform and apps on an SSD. Works pretty great.