Yup can attest to this. Spe ially if you want to get reallly good at any of those, invest in a piano, even casio will do. Hell, I use a piano app on my phone after my musoc teacher blasted me for confidently singing wrong notes 3 classes in a row. I wasnt even using the right scale and I was totally oblivious. Haha. He forced me to get a piano and voice box app after that. The voice or shruti box that helps you practice a particular scale.

A metronome app is also handy for setting correct rhythms and beats. You can flip between many different types of beats- 4 count, 3 count etc.