See answer to drainage question below, but you might consider ecology blocks for this installation instead of gabions due to likely lower expense of installation. Ecology blocks (2'x2'x3'or 6') are nearly the same size as a gabion but they would arrive on a truck and be placed with a trackhoe or other common equipment, instead of fabricated in place like gabions.
Gabion baskets would be free-draining, in fact you will likely need to put some geotextile behind the backets to make sure the retained soil particles do not migrate into/through the baskets, causing loss & subsidence of retained soil behind the backets. Note that you will not be able to control where seepage emerges from.
Consider that gabion construction costs are usually low for materials but can be high for labor.
Gabions are thick (3 ft typically). A very common use is to stablize surface water channels against bank and bottom scour.
For retaining walls not subject to inundation, keystone block (aka segmental block retaining wall) are often used in urban settings, and ecology blocks in rural/industrial settings. Block walls require provisions for drainage, unlike gabions, but that gives you the ability to control where seepage emerges.
Gabions are very useful for remote locations (ie river banks) where rock is plentiful and the only materials brought to the site are the baskets, and for applications with flowing water because they are massive and resist washout yet can deform slightly to match the channel bed.
