Hi there,
Happy to share a few thoughts/experiences of James and James. Myself and a colleague considered using them for an eComm store we run. We visited their warehouse, and received a personalised pricing breakdown for them to fulfill all of our orders and for storage.
The warehouses and offices were impressive, and they offer a reasonably comprehensive service. The pricing proposal we received, however, wasn't great. There were a
lot of hidden costs beyond the standard ones available. Things like: Account set-up fee / additional item pick fees / order branding fees / fees for each stage of goods-in, pick, pack, post (and many more). It made it incredibly hard to work out what the
actual cost per order was going to be.
When we finally went through all the numbers, and compared it to our fulfilment costs at the time, it was way more expensive, almost to the point of bankrupting the company...
We actually ended up spinning out our own fulfilment company (JustFulfil) after the interaction with them! It highlighted a big gap/need for more competitive pricing and service. Very happy to have a chat if you were after some impartial advice; feel free to drop me a message.
If you were still interested in reviewing the J&J option, I'd really recommend getting a full, in-depth breakdown of all the fees involved for your business, and compare them with your current costs, and other fulfilment services.
Hope that helps at least a bit

Joe