Tidal Mastery is unfortunately in every way inferior to the Thundering Strikes talent in the Enhancement tree, as that talent is not limited in what it applies to. The two talents stack, however. Tidal Mastery also stacks with the bonus spell crit chance from Blessing of the Eternals. Combining all three talents provides a +14% bonus to spell crit chance.
A Restoration shaman with at least five points invested in the Enhancement tree should never spend points in Tidal Mastery that can spent in Thundering Strikes in the Enhancement tree, unless the points in Tidal Mastery are required to advance further into the tree. Even then, only the minimum number of points required to advance should be spent, with the remaining points placed in Thundering Strikes.