Question about trailer wheel bearing maintenance

So the trailer that came with my Lund rebel is a shorelandr and I believe it’s a 2018 model. I’m still very new to boats and trailering so forgive me. But is this lubricating system the same as bearring buddies? And in the users manual it says when there is enough grease I can check by rocking the edge of the spring loaded piston… Is that the middle nipple that the grease gun attaches to? Neither move on mine. I’ve had this boat trailer less than a year and it was bought brand new.

Just looking for advice. Thank you!

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Those look similar to bearing buddy but slightly different. They are designed to keep a small amount of pressure in the hub to counter the water pressure when you submerge the trailer. They can be maintained by pumping grease into them if they burp a little air and deflate a bit. The center portion is spring loaded and you can wiggle it a bit to see if it is firmly on the stops or if its floating between the stops and putting pressure on the grease. If you overfill it, you will push grease through the inner seal which will likely cause a permanent leak, so be careful to stop before overfilling.

It looks exactly the same to me. It won’t rock if it is empty or super full. I go until grease squirts out or the spring compresses a little.