Interesting, first time I hear about relai. I don't know for you but for me not having a website to manage everything is a deal breaker.

I am not allergic to smartphones and QR codes but if I am forced to use invest in a particular way I didn't choose I simply avoid it.

That being said I didn't test the app, maybe in terms of features it is equivalent, I don't know.

I would still use the one which offers the choice of managing my finance with a computer. This is a very personal choice so it may not help you in doing yours.