People are generally a bit scared of changing parts of their bikes, and so they go to Halfords or their local bike shop and are talked into a new bike as "Yyou can't get the parts!" or "It's not worth repairing." This is a big shame as it's usually pretty simple and cheap to revitalise most decent old bikes upto a pretty much new performance. (Your older legs may be the biggest problem!)
The Shimano HG (HG stands for HperGlide) cassettes are generally excellent, but bear in mind the Shimano HG range varies in price/quality. A general rule is that the higher the number, the better the quality (and higher the price). Given that the numbers range in quality from around HG20 (low) to HG80+ (high), this HG20 cassette is very much at the cheap end of the HG range.
The bottom three gears (28, 24 & 21) are rivited together and so you can't split the cassette and use the cogs individually, which is worth knowing if you're of the Sheldon Brown (Google him) ilk.
I bought it to replace my worn and ancient 7-speed cassette on my old Giant Boulder. I'd been assured by my local bike shop that it wasn't worth doing and they couldn't get the parts any more and they had a great deal on a £500 Dawes etc. So I did a little research and found out it's a pretty simple job, and as ever you can find pretty much anything you like on Amazon, so I thought I'd go for it. I swapped the cassette over and bought a new chain and tried it out. Whilst I've lost my fast 11t cog, I now have comfortable two teeth jumps through 12,14,16,18 instead of the slightly annoying three tooth jump I had in my original 11,13,15,18 range. My chainset (the front gear rings) didn't like the new chain so I had that changed by (another) LBS. Having not long changed the bottom brachet/bearings, the cost mounted up, but the whole lot cost around £80. With the new chain, chainset and bottom bracket/bearings and I have a revitalised bike on the cheap.
To conclude, it's a bargain but you'll need a little know-how. A bike shop should only charge around £5 to fit it, so if you don't fancy getting your hands dirty, you don't have to.
on 5 June 2014
Th shimano hg20 7-speed cassette sprocket arrived on time and I changed it onto my Dahon vittess fold up bike, and it really works a treat. No more slipping in 7,6,and 5th gears.
on 22 May 2012
This item is exactly what I wanted. However, this is a cassette and I originally had a freewheel. This meant that I also had to purchase a new wheel.
When the wheel came though, this cassette fitted on it fine. I did however require a 3mm spacer as the wheel was 8/9 speed.
I have also ended up with a slightly loose cassette as when I have tightened the lockring, there is still play in the cassette. It makes an annoying jingling sound. I suspect this could be solved by making a DIY job of producing something to stop it moving though.
The quality of the item is great. It is made out of a standard material and is no different to other types of cassettes.
Overall, the product has met my satisfaction and I am happy with it.