I use this app! It’s based on JLPT but i think that’s really good for learning to write. Recognition/ comprehension always needs to be better than our output and this basically gives you all the most important ones. Although, most of N1 doesn’t have any option to write the kanji and some of the radicals are a bit more sensitive than others. It’s been great for me though! (Super cheap to buy all of the levels too. I think I paid £20?)
I found writing with my finger (on this) translates pretty well to writing with a pen. It does whatever you tell it to also. Meaning it doesn’t correct your lines to the best possible outcome and you see how awful you are to start with, even if it passes 
OH ALSO! It helps reinforce basic kanji orders in words. Not all of the meanings are 1:1 with WaniKani, and that can be annoying at first. But honestly, I find it super useful to have multiple perspectives on the same thing so you get a better feel for what concept a word represents not necessarily its counterpart. There’s no syncing, but I like it 
(it’s possible to skip word-only lessons if you don’t care about vocab.)
Also also, it does make you write it with no other hint than what sound it makes and its meaning. (Makes 試し and 験す a little annoying for me tbh, I forget which kanji is in the verb… 
)