It will stop working if you ever get a new camera. RAW formats are all different and Lightroom needs constant updates to support new camera models. It's a huge mess, the camera companies don't make the specs public and the formats change subtly with camera releases. Adobe obviously gets access to the formats, but open source tools are left to guess and it shows.
I just had this burn me when I got a new camera (Panasonic GH4) and I couldn't import a thing. Even worse is that I was on a road trip and didn't have a way to install the software that came with the camera (also terrible, but I took photos at Yellowstone and badly wanted to see them). As of the last week an update came out and now I'm good to go, but if you want to remain on an old version of Lightroom it can indeed be tricky.
None of the other programs you mentioned are anywhere close to Lightroom. For example, while RawTherapee can technically open images from my new camera, it displays them incorrectly. They're not even the right size and I don't want to talk about color.
You might want to play around with Darktable (http://www.darktable.org). I have no affiliation other than using it a bit. I use an Olympus EM-5 and it handles the raw files just fine.
I have an E-M5 too (great camera!), but it has been out quite a while which helps out. It's still not perfect though, the color is off a bit for the E-M5's RAW images (.ORF). The GH4 images are unusable in Darktable, they look they have been through an Instagram filter. This is straight off the camera in both Darktable and Lightroom:
It's rage inducing, but I think they are of the opinion that it's part of their secret sauce. I get the idea that they're all similar enough so that open source apps can get most of the way there, but Adobe has the full specs and is able to get them perfectly.
I just had this burn me when I got a new camera (Panasonic GH4) and I couldn't import a thing. Even worse is that I was on a road trip and didn't have a way to install the software that came with the camera (also terrible, but I took photos at Yellowstone and badly wanted to see them). As of the last week an update came out and now I'm good to go, but if you want to remain on an old version of Lightroom it can indeed be tricky.
None of the other programs you mentioned are anywhere close to Lightroom. For example, while RawTherapee can technically open images from my new camera, it displays them incorrectly. They're not even the right size and I don't want to talk about color.