My VFR aircraft has a compass, turn indicator, ASI and altimeter. I am entirely capable of doing timed turns but being VFR can't be **sed to do rate one turns. So I turn onto landmarks found under the wings.....
THe club aircraft have DI and radio nav. Mine doesn't.
Even so, turning on to 90 degree landmarks works well, and keeps heads out of cockpits. It works thus...
Turn 360 right? Find a landmark, bush, tree, field, farm, whatever under rigt wing. Turn until it is under left wing. That is half the turn. Repeat. That is 360.
Easy. Let aircraft settle down wings level. Check heading and adjust if needed. Vary as needed for lesser changes of heading.
I teach turning and acceleration errors, in gliders, microlights, and SEP. It takes about five minutes on the ground and ditto in the air. Compass not very useful in turns or other accelerated flight, read the book if you want to know why. Show the effects in flight. Job done.
I spend a lot longer on engine failure modes, how to diagnose and cope, full and the more insiduous partial. (yes, and some gliders have an engine.....)
Now my IMPORTANT instruments take up a bit more room. a proper glider vario, CHT and oil pressure and temperature, RPM. Would like carb temp, a CHT per cylinder, and EGT but can't find room in the panel or the money to buy them