NGK makes some great plugs.  I cannot say I have ever had any problems with them having used them in boats, a waverunner, and lawn equipment.  This particular plug (BUHW-2) is not as shown in the picture.  It is is a marine type plug without the electrode tab sticking out like a regular plug.  I have been running these in the same Mercury engine for twenty years.  I do replace them frequently however, as I am using this particular model on a boat that is mostly used in saltwater and the bottom two cylinders get exposed to salt water and therefore rust.  On the one hand, you could see this as a bad thing, but on the other hand could be seen as a positive because in galvanic corrosion where one metal ( the plug) corrodes preferentially to another (the block) when both metals are in electrical contact in the presence of an electrolyte (salt water), this means that it basically protects the block (since one or the other will rust first in galvanic corrosion).