In my gift roundup for Harvard Business Review last week, I wrote that the secret to buying gadget gifts for early adopters is “to surprise us with something so new that it hasn’t yet arrived at Best Buy”. The item I suggested was a keyboard case for iPhone or iPad, but true to early adopter phone, no sooner had I written down this recommendation than I decided I had to buy one for myself.

Yesterday my TK-421 keyboard case for iPhone arrived from ThinkGeek. The TK-421 integrates a Bluetooth keyboard into an iPhone case. The result is a phone with a flip-out, physical keyboard that (in theory) can allow you to type faster than you do on the iPhone’s on-screen keyboard. The case is currently on sale for $39.99, and available for both iPhone 4 and iPhone 3GS.

As advertised, it’s an all-in-one case and keyboard that turns your iPhone into something that feels more like the old SideKick (the smartphone that made me fall in love with smartphones, and inspired me to purchase the far less satisfying Treo) or the newer crop of Android phones with QWERTY keyboards, or any of the wide-orientation models of smartphones with physical keyboards. If you’re a Blackberry or Android loyalist because you can’t live without a physical keyboard, this could be the case that tips you over to the iPhone side of the street.

I’ve been dreaming about a case-with-keyboard for as long as I’ve had an iPhone, so I was eager to take this one for a spin. After 24 hours, I can say that the TK-421 feels more like a proof-of-concept than a ready-for-primetime, usable case/keyboard. It may be a worthwhile investment for people who use their iPhones primarily for texting, e-mailing and surfing, who take calls via headsets/headphones, and who always carry their phone in a bag or purse. For people who frequently use their phone as a hold-it-up-to-your-ear phone, and/or who carry their phone in a pocket, the form factor may be a deal-breaker.

We shot a quick tour of the case, and I’ve also mapped out the pros and cons below.

Here are the pros & cons:

Good things about the TK-421:

• The case fits snugly, and it’s easy to get your phone into it. Your docking port remains accessible.
• Pairing was easy to set up.
• The keyboard is nicely responsive and has the right amount of clickiness; the keys feel sturdy.
• The flip mechanism is smooth to open but stays closed properly, too.
• When I switched the keyboard off using its physical switch, and then turned it back on again, the phone stayed paired.
• Did I mention that you get an actual physical keyboard for your iPhone?

Drawbacks of the TK-421:

I’m starting with the most fatal flaws and working my way down to the quibbles.

• The case makes your phone a lot thicker. It feels quite unwieldy when held up to my ear, and since I’m old school enough to actually use my iPhone for frequent conversations, the weight and bulk amount to a major drag.
• To keep the overall case as thin as possible, the keyboard is nice and slender — which means that when you’re holding the keyboard, the phone is very top heavy. Phones with built-in keyboards typically put the guts of the phone under the keyboard, so the part you’re holding is heavier than the screen, which feels a lot more satisfying.
• The battery wears down very quickly; it seemed to die after only a couple of hours on standby.
• I had to re-pair the device after it recharged, which is a pain if I have to do it every time.
• Once you have your keyboard paired, your iPhone’s onscreen keyboard doesn’t pop up — so even if you just need to type a few keys and don’t feel like opening your keyboard, you’ll have to open it in order to type anything. You can revert to the touchscreen keyboard by turning the keyboard off with its physical switch, which is a little hard to access but has the advantage of sparing the keyboard battery.
• The extended characters are printed in a very dark red that isn’t visible in low light — which is often just the situation in which you’ll want to use your keyboard.
• The power switch is hard to toggle, which really matters since you’ll want to switch your keyboard off a lot, given how quickly the battery wears down.
• It uses Yet Another F*ing Cable to charge, and while it looks like a standard USB mini jack, it isn’t. So (a) don’t lose the cable, and (b) label it so you don’t confuse it with any of the twelve million other USB cables now found in the average American home, and (c) don’t lose the cable.
• The case makes your iPhone’s power switch hard to press.

The verdict

I’m leaving the case on for now, but my guess is that it won’t make the cut.  I suspect that the form factor of a much larger phone, plus hassle of charging the keyboard, are going to be more trouble than they’re worth — particularly since I can always use my iPad if I’m doing a lot of typing. But I’m going to give it a try for a couple of weeks, because I know it takes a little while to get used to a new keyboard, and if it turns out that the physical keyboard makes for much faster typing, I might yet fall in love with this beast. Who knows: maybe I’ll even find myself putting down the iPad and picking up the iPhone if I have a lot of typing to do.

And I’ll keep an eager eye out for an improved TK-421 that offers better battery life, higher contrast lettering for the extended character set, and/or an automagical way of switching to on-screen keyboard mode when the case is flipped closed. Unfortunately, the TK-421’s biggest drawbacks are likely intractable: I can’t imagine how to make a keyboard case with a thinner or less top-heavy form factor. Ironically, if I turn out to love using a physical keyboard, this long-awaited solution to the iPhone’s biggest drawback may have the effect of making me look seriously at Android phones.