Mike Nickeas is not a good hitter.
His .474 OPS (OBP + SLG) is the fourth-worst mark in franchise history. Here are the top five (bottom five?) Mets offensive sinkholes:
You'll notice that three of these guys played forty-plus years ago, and the fifth is Rey Sanchez, who was basically Rey Ordonez without the offense (!). Sure, Nickeas is a catcher and catchers are usually pretty bad hitters and, besides, they're really around to play defense, work with the pitchers, and so forth. Unfortunately, nobody's defense or coaching can justify carrying a bat as offensively bereft as Nickeas's, and there's little reason to think that his defense is terribly spectacular anyway.
Nickeas is with the Mets to give principal catcher Josh Thole a game or two off every week, but it's hard to fathom that a more productive backup couldn't be had for the league minimum salary. Heck, Rob Johnson, who was up with the Mets earlier in the season, is hitting .247/.287/.419 with Triple-A Buffalo, and he can even pitch a little!
With Nickeas in the lineup, the Mets are essentially throwing away two lineup spots at the bottom of the order. Outs are sacrosanct, and if the Mets really want to stick around in the National League playoff picture, they need to be a little more parsimonious with their most precious in-game commodity and replacing Nickeas with a more competent offensive catcher would be a good place to start.