I would view it as an LP jam block,blast block,or granite blocks.Granite blocks sound exactly the same as temple blocks and the blast and jams sound like wood blocks.Now a days plastic is being used more for durability,and things like ridges are being added for durability and muffeling.So I can't imagine a plastic cowbell sounding bad,so long as its made by a serious company.

A cowbell's sound is very "metallic" in nature. I would think that a plastic one would perhaps sound more like a jam or blast block than an actual cowbell. So personally, I'd still opt for a metal cowbell for the cowbell sound, and a plastic block for the block sound.

You got me all interested, so I looked for info on the Web on plastic cowbells - hardly anything. I found the auction on eBay Australia - the 4" went for $8.25 U.S., the 6" about $12.00 U.S.

About all I could find was that plastic cowbells come in different colors, which is the only reason I can think of to buy one. The auction said something about "unique plastic sound". I dunno - when I hit my cowbell, I like its unique metal sound, myself.

But they probably do look cool if they match your kit.