I'd have thought agitating 4ft trays might generate a few issues but I presume the sensitized paper needs to be processed flat. The Fotospeed price for Cyanotype II sensitizer is £142.49 inc VAT for 1 litre so I presume your new supplier is one that is cheaper than the Fotospeed product.
In terms of aesthetic challenges I was referring principally to the substantial increase in size.
Yeah 4ft trays would be slightly tricky but am sure its not too difficult. B&S can supply 1 litre for around £76 so its a no brainer really, i am getting used to this sort of cost as platinum costs the same for 10ml !! My friend will print out A1 size transparencys for £12 so i am saving money there which wil help.