If you're looking to protect your hearing, a David Clark type headset with extra foam (oregon aero kits) is the way to go. If you're looking for comfort and improved communication, then Bose does an excellent job.
The A20 is good enough that on a flight a month ago, one of the crew loaned his A20 to a check airman and a flight engineer, and they decided to buy one. The flight engineer put in an order as soon as he reached the hotel room; they're that good.
I use a Bose QC-15, with the Uflymic. It's the same electronics and the same headset technology as the A20, but a lot less expensive. The uflymic provides excellent clarity, and has options for music input, or the ability to use a backup set of earbuds. The installation is fully STC'd, and works very well (and folds flat into the flight case to keep from taking up much room).
I've used the Bose X quite a bit, and it's an excellent headset as well.
That said, you don't need to spend that much money if you're simply looking for a headset, and if you won't be using it much. I typically fly between 80 and 120 hours a month, and wear the headset for 6 to 10 hours at a time, so comfort and clarity are important. I communicate with a lot of different foreign controllers, some of which are very difficult to understand; the Bose makes understanding them much easier. It's not a necessity, however, if you're flying locally for short periods.
I have several headsets which are basic non-attenuating headsets; these are models such as the Flightcom 4DX, which cost a little over a hundred dollars when I originally purchased it. I invested in the oregon aero earseals, hush kit (foam for each earcup), and the oregon aero headband for comfort. I flew with that headset in extremely loud airplanes for hundreds of hours, comfortably (the airplanes in which I used it make a 172 sound like a glider, by comparison, so if it worked sandwiched between 4 R2600's at full bore, it will work ever so much better in a light piston single or twin. And it does.
The Bose A20 is a great headset, as are the other bose products. Lightspeed makes good headsets too; the lightspeed zulu is comparable and costs less. Several manufacturers make headsets that won't break the bank, but will serve you very, very well. David Clark offers excellent customer service and has a reputation for supporting their products no matter what (I've known people who ran over one with a car, and they still replaced it). If cost is an issue (is it ever not?), don't feel you have to own the Bose A20; you have other choices.
Having said that, Bose offers a payment plan for their headsets which makes them available to almost anyone.