My wife is using WaniKani and is quite happy with it. I had already learned around 350 kanji when I found it so it was a bit too slow for me (there's no way to "skip ahead"); I ended up plowing through the じょうよう kanji in about 5 months of intense study using a hybrid of RTK and vocabulary study sets for each kanji. If I was starting from zero or close to zero I think I would have used WaniKani instead, even knowing that it's paced a bit more slowly and will take longer.
As for getting by in Japan... it really depends on what kind of support you have. If you've got a bilingual friend or supervisor you'll be fine. Out of the 20 or so first-year ALTs I came over with, only three are above N4 level and actively studying kanji.
That said, it is an enormous help. I when I got here (with 350 kanji) it was incredibly frustrating as I'd constantly see characters I recognized flanked by ones I'd never seen. If I received an important document (car insurance, something to do with bills, etc) I often wasn't even sure what particular utility or service it pertained to, let alone what the purpose was. Going to the grocery store I couldn't read the aisle markers, let alone the packaging.
Now that I'm approaching a basic level of literacy I can navigate everyday situations so much more smoothly, and it's really empowering and exciting. The other day I hit a button on the TV remote by accident and a popup came up; this had happened before last fall but it was utter gibberish to me at the time. Now I could read that it was telling me that I didn't have access to this channel because of my basic-use TV channel package, and that I could contact my provider at the following number to discuss upgrade plans and options. That kind of thing happens on a daily basis, and being able to understand it (with a little effort) makes me feel much more like a functioning adult as opposed to just another foreigner taking a "working holiday" as an ALT.