The worst that can happen is that you'll end up throwing your phone in the trash. You'll already have backed up any data you need to keep, since you know it's going to get wiped, whether the installation succeeds or fails. The Samsung S5 you mentioned can be had for about $30, so that wouldn't be a terrible loss, considering the potential gains. It shouldn't really be a source of heartache

But I've found that, for Samsung devices at least, I've done so many that it's no longer a problem. It takes me about an hour, including the two or three times you have to do a complete reset/wipe. I use `heimdall` to flash the custom recovery, and `adb sideload` to push the new OS image. The first time I did it, it took several days.
The manufacturers certainly don't make it easy, but it gets easier every time you do it.
FWIW my favourite Lineage-supprted phones are the Samsung S10e and Note 9. The Note 10 range also supports Lineage, but I'm not going to be using a phone without a headphone jack at my time of life. Neither has a user-replaceable battery, sadly, but there's a shop in my neighbourhood where they'll replace the battery for little more than the cost of the part. These phones have SD slots and great screens. The S5e tablet also takes Lineage relatively easily, using the same procedure as the phones. I've also installed Lineage on a couple of Sony devices, but I haven't done it enough times for it to be easy.
BR, Lars