Watermaker pur 40

[Good]

Is it a good idea to install a Watermaker pur40 or is it a waste of money and for howe long can it last? can you please give me some input i have a 26 foot sailboat with 70 liters water and i think is too small for long trips, or go for flexible watertanks?

P.S the pur watermaker cost ca.1700 pound