300mg cruise is a way to hold on to all your gains. Not a safe break from blasting. The idea behind cruising is to let your body somewhat normalize. Running a level of test that will keep your levels in a range low enough to allow your RBC, Hematocrit, Hemoglobin, lipids, and other things to try and normalize to avoid extended periods of elevation. Cruising is essentially going on TRT in between cycles to avoid having to run PCT. This TRT also lets you regulate your test levels to keep them a little higher than normal without getting bloods out of hand.
300mg wk is not a good dose for that. <200 mg wk is. "real" TRT is normally in the 100-150mg wk range trying to keep test around 1000ng/dl. This is why blood work is essential for people who "cruise".