I believe the 735/735X is a USA model and isn't available in the UK currently, hence why you can only get it in 110v. The 733 model which you can get in the UK can be outfitted with a Shelix head. But by the time you've spent the £400 on the planer and another £400 on the head plus shipping from the US which would be about £60 it really isn't worth it in my opinion. At that sort of price point you could be looking at some Sedgwick or Wadkin machines for less money and they would last longer than yourself, your children and your children's children!
But I know your space is limited and you'd rather a machine that was more portable so the heavy duty equipment is off the table, As far as combined Planer/thicknessers go, Dewalt make a decent one which is the D27300. It's only a 10" capacity but so are pretty much all the over machines in this category. It's bit pricey at anywhere from £1200 to £1500. If the budget is slim I've been told before that the Metabo HC260C is a very good machine for the money (£500), You get a 3HP motor which is more than enough for most materials and Metabo build their stuff very well.
As far as Helical heads go, I'd knock it on the head. I've always thought if the machine isn't already fitted with a helical head it's not worth the money nor hassle to retrofit one into a machine. And I don't belive anyone under a professional level can benefit from having one as they won't be shoving enough material through to justify the cost of it. They make it sound like it's more economical because you do less blade changes than a standard head but being realistic, How often do you actually change your knives? Every 1/2 year? If the helical head costs somewhere around £400 and a standard set of knives costs £20 and you're changing them out every 1/2 year which is only a 1/2 hour job maximum it would take 10 years of blade changes before you reach the $400 mark that a helical head would cost before changing out inserts etc. Atleast with standard blades you can regrind them and get even more life out of them.
