Total beginner: I bought a machine but no scale, does it really matter?

Okay be gentle. I got a Breville Bambino as a gift and I’ve been eyeballing everything. Fill the basket, tamp, push button, drink. Sometimes it’s amazing and sometimes it tastes like battery acid and I have no idea why. Everyone here keeps mentioning weighing the dose and the output. Do I really need a scale for this or is that overkill for a Bambino? What kind should I get, and what am I actually supposed to be measuring? I keep seeing 18 in 36 out but I don’t even know if my basket holds 18g. Point me in the right direction. I don’t mind spending a little if it stops the random battery acid mornings.