The OP used to work for me. He was a massive fan of Sanity before he went to work for them. I think that in part that is why he went to work for them. Knowing him, I am sure that he was was not consciously doing any product placement, rather showing what he genuinely feels about the product and heading off any conflict of interest concerns others might have.
As to the practice of product placement in blog posts. This is HUGE and the way that many bloggers make their living (although less so in dev). Affiliate marketing (getting paid for links to products & services) makes up around 10% of e-commerce transactions. It's been around for a long time and is likely to continue to grow as it's one of the few directly attributable sales channels (not without its issues however).
I'm fine with people monetizing their content, especially if it's useful and ad free. What is less comfortable is where people don't make it clear that they get paid for it.
It's not 100% clear from your question whether your client is an agency (doing work for other clients) or an ordinary business whom you are freelancing directly for.
If they are an agency and the work is ultimately for someone else then this route has worked for me before...
In the UK (possibly the same in the US) in the absence of any written agreement (even if you are being paid) then all the intellectual property rights in what you create for your client remains with you.
Remind your client of this fact. And state to them that if they do not pay you, then you will be forced to contact the end-client and tell them that they are using your intellectual property without permission.
Usually just the threat of this will make your client pay up. On one occasion I was working for an agency that still didn't pay me (after I used this threat) so I did contact the CEO of the end-client, I was paid within 24hrs and the end-client fired the agency I was working for.
It's a big misconception that user testing is luxury, even for very small or one person teams. Applying some of the most basic principals can save you a ton of wasted effort. In nearly every case it will make you much more productive / efficient. The earlier you catch the mistakes, the easier to fix them.
Check out the 'discount usability' movement. Much of it is written for web / mobile development but the principles are pretty much universal and can be applied to both game design and/or interactive learning aids (in your case the tutorial).
If nothing else read up on how to run a usability test. Without even being an expert it will help you get much more out of your testing.
I understand the technology (just can't create it myself) and I've been balancing Business Requirements and User Needs for years so have that covered.
And while our idea/implementation might be easy to copy (in fact it's already been done by others in different markets) our data is proprietary and unique. And that is our real value differentiator.
The tech directors role as I saw it was to oversee the product from a technical perspective. Choose the technology, hire and manage the development team etc.
As to the practice of product placement in blog posts. This is HUGE and the way that many bloggers make their living (although less so in dev). Affiliate marketing (getting paid for links to products & services) makes up around 10% of e-commerce transactions. It's been around for a long time and is likely to continue to grow as it's one of the few directly attributable sales channels (not without its issues however).
I'm fine with people monetizing their content, especially if it's useful and ad free. What is less comfortable is where people don't make it clear that they get paid for it.