Ah, more importantly, does beer taste better out of the KK or the Zefal?
Now there's the litmus test. Pick up that gauntlet if you dare.
Sadly, I don't drink, so am unqualified to say, Ian!
I'm sorry I derailed your decision-making; it is entirely possible the things I found to be a bother won't be a factor for you. The bottles are very nicely made and work well for almost everyone who reviews them. They just didn't suit my needs for the conditions where I used them. Some of these factors might affect others, so it seemed wise to mention them.
The big issues to keep in mind really apply to all bottles:
• Will they be affected by temperature in some untoward way? (metal can become awfully hot or cold to the lips, depending, and there is the freeze-burst issue -- which can affect any overly full bottle in cold temps).
• Will they leak? If so, is there a solution and if applied, will it meet my needs? I'm now understandably leery of waterbottles of any sort in the car. Annnnnnd, not all bottles fit all automobile cup-holders.
• Will they fit your cages? If so, how well? If not, what is needed to make it so?
• Capacity. It might sometimes be desirable to fit a bottle of higher capacity in a standard cage, say during the heat of summer or where extra bottles cannot be fit, larger bottles can add needed capacity. For desert touring on the Nomad I carry 6.5l on the bike (two 1l bottles on the steerer, three 1.5l bottles on the frame in Blackburn B-52 cages), and anothter 20l as cargo. The idea of the Extrawheel trailer was to carry even more. For those tours, I need a lot of water capacity -- daytime air temps can hover between 120-124°F/49-51°C, ground temps are right at 140°F/60°C. On the same trip, daytime highs and nighttime lows can easily range over 70-80°F unless I go from the (Alvord) desert floor to the summit of Steens Mountain (9,734ft/2,967m), in which case I can be sleeping in snow and ice by nightfall -- and then all the water tries to freeze.
You'll do fine, Ian! Go for what you want and give it a try! Thousands of buyers would agree good, well-made stainless bottles can be a terrific, longlasting solution. They look pretty and give a "classic" sort of vibe to any fine bike.
All the best,
Dan.