I've been using;
This is more expensive, but works for me. The link you posted also looked fine.
I've not done any SPI/I2C work on the PI yet, I'm having enough fun in my day job..
But, if you're into hardware control (sensors/displays etc) SPI or I2C is the way to go.
These logic analysers won't replace an oscilisope, so noise/reflections will be far harder to detect - but short cables and sensilble speeds should be fine.
There are so many devices using SPI and I2C, its a great way of expanding the capabilities of the PI.
If you simply just want to connect LED and Switches to the PI, you'll only really need a Multimeter (DVM).