My two cents.
I think this feature is broadly beneficial and very consistent with good development strategy for Method.
QB is great for accounting functions, and in many cases it would be the only tool anyone would want to use. But, for order entry, production planning, invoicing and shipping it has a rather limited feature set. A good decision by Intuit in my opinion.
Enter Method as a customizable solution and we can create custom workflows for specific areas of our business. Once we convert something like Order Entry or Invoicing to a Method solution I think there are a lot of good reasons to go in 100% for one platform or the other, not the least of which is the technical issues of having potentially multiple users accessing the same data table simultaneously. For example two users entering Invoices at the same time.
We are a very small business and I can easily imagine two of us entering an Invoice at the same time or converting an Order to an Invoice while entering an invoice etc. The technical challenges to making sure this happens without corrupting the data are not trivial by any means and often it is the RDBMS that does the work of managing the record locking etc. While this can work easily with a good RDBMS doing the heavy lifting for data integrity it might be nearly impossible to accomplish with two disparate RDBMS's (QB SQL and Method SQL) held in synch by a third party (Method).
While I am impressed with the Method Synch Engine performance so far, as a user and Sys Admin I am very aware of the potential for data corruption if I start to do some weird things in the system.
As for using one system or the other, why bother entering Orders, Invoices, or other specific functions in BOTH Method and QB. That would mean that I would need to maintain two sets of screens and reports (for which QB will not be able to do what Method will be doing for me) and train my users to use both.
The advantage of having ref numbers assigned instantly in Method will be a huge benefit for me and will essentially be a 100% or more effective improvement in the overall SPEED of Method. Imagine entering an Invoice and then wanting to print it with an Invoice number in the same session, we will do this every day.
We will always reserve the use of QB for maintenance tasks, Admin fixes, etc., but it is a good idea to plan to run a business process in one system or the other 100% for a lot of reasons and I think this is a very reasonable limitation.
IMHO.
Cheers,
James