I have got one of these . Been reliable so far after a month or so of use. Has three brightness settings so you don't dazzle oncoming traffic. The brightest setting is very bright indeed. I use it as a searchlight when searching for animals in the field.
Note this one is shipped from the UK. You can buy them slightly cheaper shipped from Hong Kong.
If you are using a GPS built into a phone, you need to be aware that these can often be inaccurate by a fixed amount. For example my Galaxy S2 always reckoned that everything was about 30m higher than it was. As this was always a fixed amount (30m) it was easy to take into account once you knew about it.