Mew 👑🎩
Hey there,
Having done this before in the past, let me give you some input:
1. Do NOT make the copy company-centric. Make it about the end-user, as always.
2. Provide something of free value to your consumer that they can take action on today. Even if it's a product, identify something that is a pain point, need, or want, and write your article from this perspective.
3. Plug your product/service as naturally as possible, in one clear call to action, without excessive use of words. You want to address the solution your service/product provides, offer that solution, and get out. If the USP/wording is strong enough, they will want to learn more. These types of articles are usually top of funnel keywords, and when positioned correctly can move a user from "Educational" mode, to "Solution" mode, in which they click a link to learn all about what problem you're going to solve for them.
4. Depending on how long your sales cycle is, ignore number 3, and look at the article as a nurturing opportunity to obtain a piece of information that allows for number 3 at a later date when "Trust" has been built between you and your new readers.
5. Make sure your articles are Conversion Rate Optimization (CRO)-ed to the max for ease of use, effortless flow, mindless actions! Making people think leads to inaction.
Good luck!

Roy
A single article (sales copy or informational copy) will do very little for them. So I wouldn't spend much time going back and forth about it.
Either one is fine, they both come with different expectations down the road.
Focus on a cluster of articles you plan to write that cover each level of the sales funnel for their product.
I like to do several informational articles in combination with some more pieces of content meant for someone who is closer to buying or more aware.
Here is how I break it down:
1. People who are problem aware but have no idea what the solution would be (your clients' product type)
2. People who are problem aware, solution aware but not product aware. So these people know they need a specific type of solution but are not aware of what products exist to solve it.
3. People who are problem aware, solution aware, and product aware. These people are looking for comparisons and reviews of products they need to solve a problem but want reassurance that they are making the right choice.
Try to list content in each one of these buckets.
The articles at the top of the funnel would be meant to capture someone's email with a free thing (resources, guides, etc.) and get them to the point where they understand that your product can help them.
In the middle, we want to try and introduce them to the product that solves their problem and get them to click-through to buy or maybe get a discount if they supply their email.
At the bottom, it's all about sales. This person is ready to buy and just doing their final checks to make sure the choice they make is a good one. They are more than likely already aware of your product and will search for it by name.

Kathy
There is absolutely nothing wrong with having the first blog a review unless it's written is such a way that it will cannibalize the product page. If you think it will, then write a great product description instead.
If you decide to make it a blog post, then write it so you can rank for words like review, compare, and best, and you may even want to talk about other options to make this post very different than your product description. That post will give you the opportunity to rank on the long tail. You also make a good impression on your new client and start the relationship off on the right foot.
Going forward, you'll want to do what you suggest. Biggest mistake I see with e-commerce sites is usually because the owner wants what are essentially more sales pages that cannibalize and then don't convert near as well. I hope you don't run into that. If this is just one page, don't worry about it!

Prosky
For the sake of objectivity and industry solidarity, sometimes w the educational/informational approach we'll go the route of a compare/contrast article that highlights the client along with top 2 or 3 competitors, all in a good light, describing each one's strengths, nuances, sweet spot, etc. It gives you much more to write about and nothing evokes confidence and integrity like telling the reader that if "abc" is priority then maybe the place down the road should be their first stop…but before you decide make us your 2nd stop lol. A couple of times the competitor actually provided a link to the article cuz of how well they appeared in it. (I'm guessing their SEO was very in-house and overseen by the janitor or something).

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