Wiz,
I think you should have a look at the implications of IR35 on the tax load that your clever accounting company is doing for you and your employees.
It may also be a good idea to get written confirmation from them regarding your and your employees position regarding how an Inland Revnue audit (if it was to occur) would be handled - and more importantly who would handle it and who would pay for those not inconsiderable potential costs.
IR35 deals specifically with 'veiled' employment and the criteria are very strict and yet open to serious interpretation by IR. They may well deem that the cover of a legalistic framework as offerd by your accountants are deemed a sham and then levy full taxation and NI rates as per full employee status (which tends to come as a large shock for those that suddenly find themselves liable)
Not that I'm saying that you are in this position, but I would want to find out the bottom line if I was you. Rather than just look at the current cost savings now - what about the potential risk that may have opened up.
Various such schemes are operational at present and were at their height during the heady days of contracting office workers a few years ago. Some of them pass muster and most don't - the criteria is not usually the scheme itself that ensures success, but the actual peoples situation that work in that scheme.
eg: There are also firms that offer similar offers with most of the money going offshorte and therefore deemed not taxable in the UK by use of various mechanisms etc. Problem is that once that money is brought back onshore it is then deemed as part of your taxable liabilities (depending on overall earnings etc). However, the companies that offer those services only run with you to that point. Anything further and your on your own. In other words, Inland Revenue and the person in their own right - Scary innit?
Not pouring cold water here for you, merely suggesting that you get the backend of this thing you are in sussed out properly.
If they assure you that its all 100% in terms of financial risk with IR then ask for their QC's Opinion on the matter. If they can't offer you that then consider your options.