Ways of performing Accumulation with Dynamic Arrays

I haven't found as much time as I had hoped for to work with the Lambda editor.  How about everyone else?  I find the editor works well and both error checking and the context specific prompts also work well.  That said, I find there is a curious disconnect between the add-in's side panel and the worksheet formulas one is trying to construct.  I have yet to develop a work practice that allows me to progressively develop the formula, checking each step of the calculation as it is created.  When I am in a VBA environment, the ability to step through the calculation using F8 is a lifesaver -- which probably demonstrates my shortcomings as a coder.

I do wonder whether the environment for creating Lambda functions on the worksheet could also be improved.  After all, creating formula-local names using LET is now second nature.  Would it be possible to allow workbook-scoped names to be defined in a similar manner?

Does anyone have insight as to the reason that the performance of the Lambda functions can be underwhelming?  It could simply be the lack of 35 years of optimisation but I also wonder whether the memory management required to support recursion is the source of problems.  Certainly Charles William's ACCUMULATE function was lightyears ahead in performance and, since converting flows to balances is so central to modelling, I would like to see it as an Excel built-in function.

Talking of FastExcel, Charles Williams has given me permission to upload a newly developed runtime version of the addin, if anyone is interested in trying it.  It appears that the addin and the Excel workbook should be packaged as a zipfile and used within the same folder,