I enjoyed BUILDING the Beta 22 way more! The Beta is just an awesome piece of gear. The M3 is super good too. But the Beta is over the top in terms of electronic goodness. There's more to this hobby than the sound. I think the "object-ness" of the gear can be a pleasure in itself, and building something with as many parts as the Beta is a good way to while away quite a few hours during wintry evenings. Take your time in building; it's a craft like cabinetmaking or weaving.
HOWEVER: if you have never soldered very much before, the Beta might be daunting. There is A LOT of soldering on this thing, and one cold joint or solder bridge where there shouldn't be a connection can prevent it from working and can be hard to find among all those many solder joints.
So in the case of novice builders I would warn against the Beta; the M3, or the CK2-III would be a better choice.
http://www.amb.org/audio/ck2/ the CK2-III is pretty easy to build, even easier than the M3 and offers similar performance.
Will you hear the difference? I dunno. They are real damned close.
BUT- the Beta definitely can drive HE-6's and the M3
can't. The M3 driving the HE-6 clips audibly at levels I would find "moderate to somewhat loud"-
Now you may never have a pair of HE-6. But then again you MIGHT. And maybe the HE-99,000 will come out offering class-beating performance at some middling price point but require gobs of power the way the HE-6 does. You never know. (FYI, I found that the CK2-III CAN drive the HE-6's to loud levels.)
The Beta 22 is the kind of thing where you feel, gee, this is likely about as good as it gets, I won't have to worry about upgrading my headphone amp maybe for years and maybe for MANY years. And if you build it yourself there is good
value, too, even if it costs a few dollars.
I think the place to look for savings with a Beta 22 is the CASEWORK. I bought a Par-Metal case which is nice but not real fancy or anything. And it cost over $100. And you can spend even more! So maybe try to do something with wood lined with thin aluminum sheet to shield against electric fields like AC buzz. Or some other creative do-it-yourself solution. Like, buy an old DEAD power amp for $7 on eBay and gut it out. A power amp will have a minimum number of holes cut in it, allowing you to creatively re-use the chassis.
And FOR SURE build a 2-chassis Beta22, I made the mistake of building a single chassis and had to enclose my power transformer in an inner steel chassis or there was hum. I had my Beta as a 2 board amp at first: no hum. Going to 3-board "active ground" setup, and there was HUM. The 3-channel version seems real sensitive to the magnetic field from the transformer. For your power supply, use a more utilitarian cheaper STEEL enclosure and tuck it away out of sight like a wall-wart when using your Beta22. Steel is good, it contains the magnetic field from the transformer and is cheap.