Good depending on needs
I have used this product a few times to extend putters as I have an addiction to buying 2nd hand putters on eBay, often needing to extend them from 34" to my preferred 35". Each time I have only extended by 1 inch, and for this purpose it works very well, and is far easier to cut than steel extensions (if like me you have limited tools at your disposal). If you are looking to extend a putter by 2" or more, I would be a bit wary as it could then be a bit flexible, and I'm not sure I'd be confident extending an iron shaft as the force of the swing is so much greater than a putter - it's a very stiff plastic, but it's still only plastic. But for purpose of adding an inch or so to a putter, I find it just the job.