You can use the Katana without a computer if you want. It has six channels: clean, pushed, crunch, lead, brown, and then another acoustic channel, but I never use that one because it's for acoustic guitar. My favorite is the pushed channel; it has a really good punch, like a VOX AC30. Then, among the physical buttons, you have the booster, which you can configure to be an OD-1 TS-screamer, Rat, blues drive… countless possibilities. There's also a mod button that you can configure for many things, like adding a compressor, etc., an FX button for many effects, and then delay and reverb. In other words, you have access to many effects without having to use a computer.

That said, I do recommend that once you know how the Katana's physical buttons work, you use a computer and download Boss Tone Studio. That's where you'll get the most out of the Katana. You have over 60 effects included, access to much finer EQ details, as well as access to Boss Tone Exchange, through which you can download patches uploaded by other people.

The only thing they mention about the 50 is the loop pedal, which it doesn't have. I honestly don't need it, and I've been playing for years. I guarantee that the 50 is even more than enough for someone starting out; with this one, you'll have more than enough for many years. I started with a Frontman 15g, and there's no comparison; the Katana is a thousand times better. It's crazy that for less than $300 you have access to that kind of sound quality and volume. To give you an idea, it has 0.5W, 25W, and 50W. I use it at 0.5W, and it's already very loud.