I pretty much agree with Jazzafish,
I have a 20litre mash tun, and it works fine.. I batch sparge in it, but have to do a couple of rounds. But I do wish that I had a bigger tun and will
probably upgrade when I can be bothered or I find a cheap bigger eski. I struggle with "big" beers.
But... for $25.00 it will do just fine and give you time to search around for a bigger alternative if/when you think you want one.
The 27litre pot would be full to the absolute brim or a little over for a 23litre batch.. sorry.
Of course, there's no rule that says you have to make 23litres... make a 19 or 20 litre batch and it would do.. you'd have to watch it for boil overs pretty carefully and you'd most likely wish you had a bigger pot... but it'll get you going. Like Jazza said, if you find yourself a bigger pot later, then you downgrade the 27litre to a HLT. No loss.
I say go for it... but be aware that you will probably want to upgrade at a later date.. which you probably would no matter what you got
Thirsty
(or what the other guys said, jeez I'm a slow typist)