I personally wouldn’t buy lifetime.
I started around April and when I got my yearly subscription this was the cheapest option (knowing Lifetime sale would only be in December). I plan to finish may to july so buying lifetime just isn’t feasable anymore.
There are also other reasons to not buying the lifetime membership. I think that having a lifetime membership will actually make you progress slower, because you don’t have to pay for the time you spend. Also, for lifetime users it’s “okay” to make a 2 year break, because they still own WaniKani after that. What these people forget is that they virtually reset their Japanese.