I've seen affiliates doing exactly that. Generally speaking, promoting only one electronic cigarette brand, even if it's by all means great, won't make you credible for more than one reason.
1. You are here to serve your visitors, not one company. Ok, you are here to make some money in the process, too. But you won't make much unless you provide some value to your readers. Promoting one e cig brand, however great it may be, makes you look as if being here just to take your part of the cake. I sincerely hope it isn't so because e-cig is a fantastic product in what it can do for the health of smokers.
All NRT therapies with their 5% or less success rates don't even come close to e-cigarette switch rate. (If 5% is a success, then I am Sharon Stone, pleased to meet you.) That' why the affiliate endeavor in this case is a worthy job that goes widely beyond the personal benefit of an affiliate. You are promoting superior products that will have more and more users as the time goes by.
2. People normally have different tastes. Even if you are trying to sell to one segment of users – say, single women 25-35 - it's not just one brand you can offer to the group. Some of these girls would be delighted with Vapor Couture, others will be perfectly happy saving their money and enjoying highly customizable design that Premium Electronic Cigarette can offer.
3. It's not just a matter of taste – other settings are there that make people different. Just to name a simple one – some folks are alergic to PG (Propylene Glycol). Most companies have their cartridges (cartomizers) with either pure PG or PG/VG liquid. So, you basically need to have an affiliation with a reputable company providing VG e-liquid in their cartomizers (like Prosmoke) or VG-liquid separately if we are talking about eGo type, APVs or similar e-cigs.
4. People may have other concerns: Some want their e-cigs completely manufactured in their country or at least having a home company control the foreign manufacture.
5. They may also have different priorities related to what they spend their money on – some will look for more affordability, some for higher quality.
one e-cig brand won't make your content
rich. Lacking content won't push you high with search engines. Besides,
what value are you providing to your readers? Most of that info you are sharing
can be seen on the homepage of the company itself and it is normally higher
ranked in the search engines than your little website. (And, by the way, forget about Google AdWords, at least for the time being. Google is heavily prejudiced against e-cigarettes.)
7. Last but not least, it's a matter of your independence as an affiliate. Never put all your eggs in one basket. The company may go down, the affiliate program may go down for whatever reason, like it happened to one I was affiliated with.