Ask it in the Homeowner's or Major Remodeling Forum.
Units are small and modular, so walls can taper, turn, wrap and curve.
You can't mix and match manufacturer's systems. Block systems that use metal pins to tie blocks together can be a challenge to line up exactly. More expensive systems tend to be stronger and stack higher. Follow all rules for landscape fabric, drainage and backfill. Use manufacturer's calculators to determine how many blocks, pins and tiebacks you'll need.