This is a very reasonable worry. I have bought and owned many, but quite a lot of them have been difficult to maintain or repair, and some have indeed ended up propping a door open.
However, this is not necessarily always the case. The Roland units were extremely well-built and many units are still going strong after decades. Plus, you can still get repairs, spare parts, even new tapes.
Ditto for the Echoplex. My dearly-missed EP-3 was well-made, and easy to maintain and there are plenty of vendors out there who sell parts and tape cartridges.
Currently, I have four tape echoes, one relatively modern and three vintage. The oldest is a Brennell unit which may actually have been custom made. I can find no record of the company ever having made such a thing. It is a tube machine and was originally made in the late 1950s or early 1960s. It is in dire need of restoration. It works… barely.
The other vintage units are Space Echo knock-offs from MultiVox. One needs work, and the other could use a bit of maintenance. Tapes for these units are still available, too. Like some Roland’s, they feature echo and reverb, but also sound-on-sound. They aren’t as well-made as a Space Echo, but they are by no means lightweights, either.
Finally, I have a Fulltone Tube Tape Echo. This is a stunner. Ostensibly an Echoplex clone, it is beautifully made. However, if you are in the market, be prepared to buy it new, as Fulltone won’t even sell tape cartridges to secondhand buyers.
There are other new(ish) units out there. I had a couple of T-Rex Repicator Jrs, but the tape width was narrow, and I could never not hear the tape splice. Still, it had tap tempo, and that was pretty damned cool.
There is also the lovely EF-X2 from Echo Fix, which has much of what is most loved about the Space Echo, but in a new machine. I have not seen one in real life, but a friend of mine recently bought one, so I hope to eventually get the chance.
There is nothing quite like a tape echo. You need to be prepared for the quirks of whatever unit you buy, but if you get a good one, you’ll wonder how you ever got along without it.