Reading the new online version of Toolbox 2 is a rich experience. I have had access to these resources on my computer for many years, and have looked at them frequently, but helping to proofread the themes as Matt converts them to online format I have been reading every single word and every embedded resource and it is truly an illuminating experience. I've been especially interested to note that many of the linguistic terms people associate with more recent scholarship, terms like "zero allophone" and "default grapheme", were introduced to this community by Real Spelling many years ago.  The precision of language found in TBox 2 is particularly clarifying.  Take a look for example, at the small extract in the Theme 2E, page 4 of the new online edition "Defining the phoneme, the unit of phonology."  It's an extract of the Real Spelling ebook on "Phonetics and Phonology: a crucial difference." If you find yourself uncertain about how to explain phones and phonemes, you would do well to study this!

Then there are the myriad fascinating examples.  In Theme 2d on Homophones for example, I learned that the words <oar> and <awe> are homophones in Received Pronunciation of British English. I found this so surprising that I had to check it out in the OED. Sure enough.

I'd be interested in knowing what delights and profundities are affecting other subscribers, either new discoveries or rediscoveries.

Of course, Toolbox 2 is a historical resource.  And actually, as with any resource, you may also encounter things in it that surprise you and don't seem to line up with evidence you have found.  These provide excellent opportunities for new scholarship and deepening understanding.  

In Theme 2d, page 13, for example, we see a chart indicating that the phoneme / / is never written medially with < ow >.  The word < bowl > contradicts this statement.  Investigate words with < ow > and think about how you might modify this chart in your own work. Is it just a matter of changing the word "never"?  As an OG tutor, I taught students that the grapheme < ow > spelled / / only at the end of a word, unless it was followed by < l > or < n >. But what do you find when you look up words that end with < owl > pronounced / oʊl /?  Is < bowl > the only one?  Why is it spelled the way it is?  We don't need to call this out as an exception - there's a reason for the evolution of this spelling.  
From the OED online:

The normal modern spelling would be boll n.1 which came down to 17th cent. in sense of ‘round vessel’, and is still used in sense of ‘round seed-vessel’; but the early Middle English pronunciation of -ōll as -ōwl (compare roll , poll , toll , etc.), has left its effects in the modern spelling bowl in the sense of ‘vessel’, which is thus at once separated in form from other senses of its own (see boll n.1), and confounded with bowl n.2 a ball, < French boule.

I don't understand the part about the early Middle English pronunciation, since there is no IPA representation.  But it's clear that differentiation of meanings played a role in the history of the < bowl > spelling.  And certainly an investigation of the < bowl > family (or families) with word sums and matrices would be more interesting than putting < bowl > down on a chart or list as an exception. Such interesting compounds!

And then what do you find when you look at words ending with the letter sequence < own >?  How is structural understanding helpful, and necessary here?  Perhaps the most generative thing to teach here is that we need to look closely at evidence and pay attention to both structure and history in analyzing spellings. Think what great investigations this might inspire!