I bought this Shake Awake to replace my old Seiko Vib alarm clock. I am very disappointed. Shake Awake never woke me up because vibration/alarm shuts off after 30 seconds. This is not long enough for me to wake up. It is also rather large to place under my pillow. I use thin pillows (big pillows hurt my neck) and this clock feels like a big stone under my pillow.
The vibration power is not too bad (probably as strong as the ones in cell phones), but the pulsating vibration makes it feels milder than continuous vibration and 30 seconds alarm is simply too short. I am also not too crazy about how this clock looks. It looks and feels cheap to me. To be fair, this clock does feel quite sturdy. Snooze and display backlight are also good features. It is "portable" but a bit too big and heavy to carry around in your pockets with one AAA and two AA batteries inside.
My old Seiko is much much better product that actually wakes me up with one minute alarm/vibration. It is very small - about the size of a credit card or a pager and fits right in the coin pocket of my jeans. It uses only one AAA battery to power both clock and motor. The battery lasts one year (it usually lasts more than two years for me). It is still going strong after nearly 20 years of abuse but the tiny buttons became weak and I have to use the point of a pencil to press the buttons to change alarm time, which is a bit annoying.
After the disappointing experience with Shake Awake I got an updated version of the Seiko (SQ617K). This is a true gem. They did a really nice upgrade on this model. It comes with two timers (count down up to 19 hours 59 minutes) that can run simultaneously with daily alarm. Alarm and the timers are very easy to set and now with bigger buttons. It also has a large tactile alarm on/off button and let you know if the alarm is on or off by short vibrations. This feature allows you to turn the alarm on/off inside of your pocket without looking at it. It also comes with lanyard hole.
Now I use this for both waking up and as a meditation timer. It seems Seiko does not market this outside of Japan and I had to have my family send one for me. I really hope they will sell this in US someday so that people do not need to endure not-so-great products like Shake Awake. I have searched around on the web for a long time and I believe this is really the best portable vibration wake-up alarm/timer in the market. It's in the same price range as Shake Awake (retailed around $25). It comes with a manual written in both Japanese and English. You are lucky if you have a friend in Japan who can ship this to you.