Thank you for the kind words, and also an accurate description of "things". I'd like to make some comments.
First, regarding High Sierra, except for it being slow at starting up either of my Macs (faster on my mid 2017 13" Mac Book Air than on my late 2012 Mac Mini; both have internal SSDs), or switching from one startup "device" to another, I am having no issues at all with High Sierra. As expected, the two internal SSDs are formatted as APFS. For both of my external devices (512 gig Samsung 850 Pro SSDs), there are 3 partitions on each: two of the partitions, formatted as APFS, are for the SuperDuper! backups for each of my Macs, and the third partitioned, formatted as MacOS Extended, contains "other stuff" (like past tax returns, photos, movies, TV series, etc.). Of course, I make a concerted effort to keep both of my Macs "lean, mean, and clean", and this includes keeping all of my software up to date.
I actually have a good amount of third party software on both machines: VLC, Transmission, Quicken 2007, Quicken 2017, Onyx, Tech Tool Pro, Office 2016 (actually only Outlook 2016, Word 2016, and Excel 2016), SuperDuper!, AppCleaner, GrandPerspective, Malwarebytes (not all the time "active"), TrashIt!, GrandPerspective, etc. Except for a minor "glitch" with Quicken 2007, all of my software functions fine (I am not including my browsers Google Chrome, Opera, and Firefox, as they tend not to depend on the OS).
I cannot say about issues with external HDDs formatted as Mac OS Extended, so maybe someone else can "chime in" about such an environment.
Secondly, I know quite a number of folks complained to Micromat about having to pay another upgrade fee to upgrade from V9.6 to V9.6.1, and while I can somewhat understand such "gripes", to me it was justified. As it is, Micromat, Shirt Pocket Software (developers of SuperDuper!, and Bombich Software (developers of Carbon Copy Cloner) needed to devote significant time and resources to come up with fully functional High Sierra compatibility. Yes, Micromat is the only company out of those 3 that charger for the upgrade, but based on what I read, it was worth it. And to me it is worth it, as I depend upon Tech Tool Pro (along with Onyx and SuperDuper!).
Third, yes, it is not good (in fact "bad") to optimize/defragment SSDs). I of course have never done it. Also, I think the reason why Micromat still has those features included with Tech Tool Pro is that there are still a number of folks that have traditional HDDS as internal drives. I myself never believed any of that "talk" about not needing to defragment/optimize HDDs. I always did it with mine, and I really did not seed any decrease in the useful life of such HDDs. (I've actually been hearing the same BS about Permissions Repair. Unfortunately, both Titanium Software (the develops of Onyx) and Micromat no longer include that feature, at least with the High Sierra versions of their products. It actually can still be done, but requires the use of Terminal).
It seems like you have the "advanced" features of V 9.6 covered, although I've never used the feature to check my internet speed (there are other free products available that can do that very well, and my speed with Comcast/Xfinity and my Telephony modem is fine).
The latest version of Tech Tool Pro is V9.6.1, and it is fully compatible with High Sierra (Disk Warrior and Drive Genius are not). I suspect there is no harm in upgrading, but I am unsure if the upgrade fee from V9.5 to V9.6.1 is $19.99, or $29.99. When and if you do upgrade to High Sierra, however, I suspect you know that an upgrade for Tech Tool Pro will be a necessity.