You should use it as otherwise making things work properly across all types of devices in a meaningful way is a lot of hard work and I've seen developers try and be 'smart' about things and get things buggy on various smartphones (especially Android) and they don't know how to fix it. Reason why frameworks are there is to make responsive web stuff work properly across many different devices. Use it. It's good for you. Also remember that you are likely to have to recode a web app every 2-3 years or so, for one reason or another, unless you keep it all really, really simple.