Even if you do not disclose sponsored reviews, most websites will have a sponsored review section. This will indicate to your reader that you do write sponsored reviews. If you do not disclose sponsored reviews, may be a few of your readers may get upset. But I guess they really can not complain much about it, if you are honest in your product reviews.
Creating good products that are well made and polished require a ton of time and additional resources (like design, content, etc.). There’s a lot of ‘hidden costs’ in both time spent and the contractors to collaborate with. Selling your own products on your site also brings up problematic issues like payment gateways (how are you going to collect payment?), shipping (how are you going to mail or distribute the products?) and taxes (oh man, don’t even get me started with that one!).
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.