Lionel made the original 12062 and then updated that same accessory but kept the same SKU.  The originals were Series 1 and the latter Series 2.  Underneath the Series 2 has one screw in each corner of the gearbox covers.  I have a Series 1 and experienced no issues after several years of service.  The gear inside the gate on series 1 strips if the arm is restrained when actuated or forced up or down by hand.   Parts for them are hard to come by.

So which one is the better one? Series 1??? or 2???

Series 2 is less prone to failure.  That is why they changed the design.  If you buy a fully functional Series 1 then caution is necessary around pets and small children.  

Thank you for the knowledge! much apprieciated!