Yes, MODESTER is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, D 2, E 1, S 1, T 1, E 1, R 1.

Is it a valid word?

MODESTER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

marked by simplicity; having a humble opinion of yourself
not large but sufficient in size or amount
free from pomp or affectation
not offensive to sexual mores in conduct or appearance
low or inferior in station or quality
humble in spirit or manner; suggesting retiring mildness or even cowed submissiveness
limited in size or scope

Also: small-scale, pocket-size, pocket-sized.