Basically the shortish version: SWK is pushing SPS as hard as they can because they get a recurring commission on them. Sometimes they push them even when it's not a good fit.
The cost to move over from an on premises package to SPS starts around $12,000 and that is largely the cost to SWK to redo the maps and an amount to SPS for testing. In my experience and having had a few conversations with SPS and a couple of clients on their service, they will usually waive the setups for the SPS portion, but they won't usually waive the SWK portion since they have to write a check to SWK.
The one case where we started up using SPS, the customer was completely unsophisticated and didn't know what EDI was other than their vendor was strongly encouraging them to use it. In their case, it made sense because if they have a problem they call SPS and SPS takes care of it completely.
The other case was one where for business reasons they were looking at migrating to an enterprise level EDI translator (moving from Trusted Link to Delta /ECS) and the cost was going to be close to $30k. Basically in their case SPS waived their setup fees and SWK agreed to decrease theirs. These guys are high volume too, so their getting a decent sized discount on their monthly services. The break even point is seven years with no interest factoring.
In my experience and from what I've heard from others is that unless you have a small number of trading partners, you can usually double or triple the implementation time they tell you. They do a good job. It's just that some times, depending on the trading partners and the number of trading partners, it can take a long time to get all of the trading partners completely remapped.
In Diane's case, they weren't using very many trading partners. They wouldn't get a large discount from SPS. They're not fully up and running on QualEDI. The monthly costs were going to be significantly more with SPS than what they were currently paying. It probably doesn't make sense.
SPS does an analysis of your current transactions and calculates a monthly fixed transaction fee based on expected activity for the customer. They reset that fee at the end of each year, although you can ask for an adjustment any time within the year if you foresee any huge changes. They handle a lot of the hassle work with EDI.
I did say shortish.