Use 'serviceable' to describe something that meets basic needs without frills. The rented room was plain but serviceable for his short stay.
Pro Tip 2/3
Not Premium
'Serviceable' implies functionality, without suggesting high quality or luxury features. She bought a serviceable phone with just the essential features.
Pro Tip 3/3
Second-hand Acceptable
Describes used items that are still functional, despite not being new. His serviceable jacket came from a thrift store.