Having applied for (and received) a few Visas myself, if I’d known about or could have afforded a service to take ANY of the hassle out of it for me, then I would have gladly considered it.
I’ve not even read the article, but I’m not sure I even feel they or STW are obliged to promote a link to the DIY Visa portal, so long as article isn’t trying to suggest there is no other way to get one (e.g. any inference that you HAD to use their services would be super dodgy).
They offer a service, at a price, if it appeals to you, what’s the problem? Frankly if you want a VISA and were not already aware that there was a DIY route then perhaps you are the sort of person who needs a bit of hand holding anyway (not meant to sound derogatory, just saying there is a legitimate market for hand-holding…)