I had attended couple of gadget events, the company used to give a device to selected 'reviewers' including this site webmaster (Tony John) if he attended the event. They don't give it to all but few selected to review the product. The company will give the device immediately or send it by courier to address. They also give 3 weeks to 3 months time to complete the review. They do follow up with reviewer's as well.
The first article of xyz gadget will be normal detail of the device including specification, feature, price and launch or release date etc. Those detail published doesn't mean completed the review of the product. Hands on review is entirely different than the first post published with the gadget specification, feature, price and launch or release date etc. to reach the audience and grab the visitors' attention.
It takes around 3 to 5 days to experiment the device in a different perspective and publish the gadget review online as second or third post. Sometime, it takes more than a week to review the product as well. Some gadget review needed either more than 2000 words in a single post or 2 to 5 different posts with different points for the same gadget review. In that, many review points would have covered than just specs, feature, price and launch or release date etc. I mean, the review article (later one) will have various points pertaining to hands-on honest review. Those review might have covered entire or little pros and cons of the gadget, unboxing detail, inside box's peripherals detail, quality of the each pieces, different result from different function and angle, various feature testing within and its steps, comparing similar products and its points, images, videos and on.
There are many tests and points to cover to furnish the complete review result of the gadget. Some reviewer's review the product just 25%, some 50%, some 75% and very few 100%. It is all depend on the expertise reviewers. The best or better review done by the reviewer's, the best chances to get reviewer's reputation and attention from the respective companies and mass.
Finally, yes, the gadget review is worth, many used to search online for 'review of the product'.