I was wondering if there is any problem with using a small flash drive like a "cruiser fit" as the main HDD for Linux.

Should work just fine, many people do it.

I am scared of exceeding the re-write limit. I assume something like this isn't as robust as an SSD, but is it good enough?

Yes, not a problem. The rewrite limit is a solved problem.

For most quality brands, you can continuously rewrite data for over a century and still not fail due to bad writes. For bad brands you can only continuously rewrite data for a few decades, which probably is far more than you are doing.

For any particular brand you can look up endurance tests, and some brands --- especially no-name brands --- are particular bad for drive failure. It usually isn't the rewrite limit, but instead is failing due to other hardware problems.

I have done this, running an entire VM off a USB drive. It works, but for the love of god spend the extra fifteen bucks to buy the fastest USB 3 drive you can find. SanDisk Extreme is a good choice.

(If somehow you do not have USB 3 ports, don't bother attempting this.)

I'd actually be more worried about the accidentally getting stepped on problem. Backup regularly.

I have done this, running an entire VM off a USB drive. It works, but for the love of god spend the extra fifteen bucks to buy the fastest USB 3 drive you can find. SanDisk Extreme is a good choice.

(If somehow you do not have USB 3 ports, don't bother attempting this.)

I'm looking for a small sized one that I can keep plugged into my computer.

I'm not sure how to judge performance, are the small ones less performant than the big ones?

Does this one seem ok?

https://www.sandisk.com/home/usb-flash/ultra-fit-usb

I have done this, running an entire VM off a USB drive. It works, but for the love of god spend the extra fifteen bucks to buy the fastest USB 3 drive you can find. SanDisk Extreme is a good choice.

(If somehow you do not have USB 3 ports, don't bother attempting this.)

I'm looking for a small sized one that I can keep plugged into my computer.

I'm not sure how to judge performance, are the small ones less performant than the big ones?

Does this one seem ok?

https://www.sandisk.com/home/usb-flash/ultra-fit-usb

Write speed is what matters. I looked and that drive in 128 GB benchmarks around 68 MB/s, which is pretty iffy in my book. I'd prefer to be above 100. But from what I can figure, you will have to go to a physically larger drive to get better performance.

Is there no room for a second internal disk? My notebook has two SSDs.

While what you want to do can be done (I've done it), I am very not much in favor of any idea that involves "USB", let alone USB pen drives. USB nowadays has reasonably good bandwidth (about 2/3 as much as SATA 3.0), but it still sucks in terms of access time (tell me why, I wouldn't know, must be the protocol?). Even iSCSI, which goes over network (network is supposedly as slow as you can get?), is way better than USB drives on my system (although, admittedly, iSCSI is making really hefty use of caching both reads and writes, to a sheer stunning effect, so the comparison may not be 100% fair).

USB pen drives are better than they used to be, but the flash memory that is used for them is still the cheap rubbish the manufacturer has left over after producing "real" SSDs. Basically what's not good enough to go into a "real" SSD goes into a pen drive, rather than the trashcan. Also, although write cycles are -- for every normal use -- not so much a problem any more nowadays, broken controllers and physically broken pen drives still are, and will remain to be.

I've broken the plug on a pendrive more than once by making an inconsiderable move and breaking the plug off (or the plug being visually "OK", but non-functional). Happens mostly with my knee on drives plugged into the desktop computer (which is under the desk). But I've also occasionally caught a pen drive plugged into the laptop with the sleeve of my shirt (luckily so far without breaking anything). All in all, it's not too thrilling an idea for anything that is kinda important.

've broken the plug on a pendrive more than once by making an inconsiderable move and breaking the plug off

That's why I want one of these pico sized ones. They should be pretty hard to break once they're plugged in, because they don't really stick out. The small form factor seems more important than performance with regards to that.

I decided to get the 64gb sandisk ultra fit