I was pretty excited about Amazon.com's supersized Kindle, the DX model it began selling last week.

But after spending a week fiddling with a test unit loaned by Amazon I'm not sure it's worth the extra $130 over the price of a standard Kindle. The DX costs $489 vs. the standard $359 model.

Amazon is aiming the DX particularly at college students. It's working with textbook companies and plans trials at universities around the country this fall.

I wonder if students would prefer the smaller Kindle, though, and not just because it's less expensive.

The DX screen is about the size of a hardback book, compared with the paperback-sized screen on the standard Kindle.The DX also has double the storage -- 4 gigabytes -- and on-board support for PDF documents. They both use 3G wireless service to download books, newspapers, blogs and other material.

But there are some tradeoffs for that bigger screen. For one thing, it seems to burden the processor more -- page refreshes seem slower. A spokeswoman said the DX uses the same processor as the smaller Kindle.

Amazon also added an auto-rotate feature, so the screen shifts to a horizontal mode when you turn the DX sideways. I found it maddening. It takes just a little too long to rotate, and you have to really tilt it upward sometimes to get the rotation going.

But the thing I missed the most was the compactness of the previous Kindle, which has a better blend of power and portability. It's small enough (8 x 5 inches) to stuff into a large pocket and easily hold with one hand. The DX, meanwhile, is like a thick clipboard that needs backpack or briefcase to conceal.

Even though it's more of a two-handed device, the DX only has page-turning buttons on the right side. The standard Kindle has page buttons on both sides of the screen, so you can read while holding it in either hand.

Maybe my problem is with other comparisons prompted by the larger device. The slim, standard Kindle is kind of a marvel. On such a little gadget, it's a surprise how readable the screen is and how much technology is stuffed inside.

The DX brings to mind slate-style PCs that are just a little bigger (the DX is 10.4 x 7.2 inches and 0.38-inch thick) but more powerful, with color screens that take pen and finger input. That may not be a fair comparison -- the Kindle is only trying to be a reading device and it's thinner -- but it's hard to shake the association.

If you're going to carry around something this big, and devote that much space in the backpack, you may expect more than a black-and-white reader with a rudimentary browser, a weak MP3 player and an oddly spaced keyboard.

Newspapers are especially interested in devices like the Kindle that can deliver their content to subscribers. Some readers say they like papers on the Kindle but I think it has a ways to go, and the DX isn't much better.

The problem for me is that you can't quickly scan and skim across a page -- the Kindle presents one story initially, or you can click a few times to see the first sentence and headlines from six stories at a time.

The built-in PDF software could help here, though. The DX can display the PDF of a full newspaper page, big enough to read everything, if you squint a bit.

Perhaps I'm jaded or too caught up in the handheld gadget thing.

I've got to say that when I showed the Kindle DX to a group of people who had never seen any Kindle before, they were impressed and excited by the possibilities of the device. They didn't mind the size or miss the left-side button.

Maybe there's demand for a whole lineup of Kindles -- coupes, sedans and pickups, whatever size you need -- but hopefully the big ones will get more powerful engines. And they all desperately need lights, so you can use them in the dark.