for $35 - Microcenter has a 256GB 3.0 flash drive as well as a 256GB SSD. When I check the speeds, they appear to be very similar. I'm under the impression flash drives last longer (given both products are the same level of quality) - and flash drives are portable, so they might be the better bet.
What do the experts think?

Are you just looking to store some files on it or are you thinking of actually running an OS from it?

First to address the connection type. If you're considering running an OS from USB, just know that any device connected this way will operate at about 1/4 the speed of a SATA connected SSD and about 1/10th as fast as an NVMe connected SSD. Rated speed of USB doesn't mean it'll perform well for the amount of random IO that an OS requires. USB will be a bottleneck.

And no, the devices will not be anywhere close to the same speed. Just because a flash drive lists a certain speed, doesn't mean it'll actually perform anywhere near that in the real world. They'll list some crazy speeds like 130Mb/s but what they don't tell you is that the speed is only for the first 50mb of cache after which it drops off to around 40mb/s write speed. Even SSDs get this effect as they have a limited RAM buffer, followed by a somewhat larger SLC NAND buffer but then ultimately have to move data to the much slower MLC NAND. But, at least with the SSD you'll get a few hundred MB before the write speed drops and typically have multiple NANDs it's writing to in parallel.

Then there's the fact that the flash drive might be a fake altogether. Microcenter is usually pretty good, but Amazon and eBay are just full of thumb drives with spoofed sizes.

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Data Medics - Hard Drive, SSD, and RAID Data Recovery Service Company

Second everything data-medics says, plus to add that most flash drives are made from inferior quality NAND chips. So the comment that flash drives last longer is not true. They are also prone to connectors being broken.

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HDD, SSD, Flash and RAID Data Recovery
Founder of The Data Recovery Professionals Group