i used to use the cheap big back grips, they just felt cozy, pain in the ass to keep using. if i want to alleviate forearms on bicep lifts, OPEN and SPREAD YOUR FINGERS and PALM IT. works wonders. I've had tendonitis in my forearms, golf, and tennis elbow at diff times. if forearm tendonitis is killing youf or biceps, start lifting heavier in your back exercises and let forearms have a break for 3-4 weeks.
i have good sized forearms people used to call me pop eye, never liked being called that. but they were to my advantage in muay thai fighting. genetically, but what really helps them grow is grabbing a bench olympic bar and doing motorcycle revs' (if youve ever rode a dirtbike) and let it roll out into your fingertips upwards and toward you , upwards for brachial ... add weights if its too easy, i usally do 3-4x 20 1x per week but mine are bigger than my biceps rn and tris post hospital in july, so it looks a bit ridiculous. plus ive torn both biceps and a tricep, makes it interesting....