Inbuilt heaters do work but they're not quite as effective as a similar sized freestanding one. The freestanding ones circulate the air better but they have the other disadvantage of taking up valuable space. If your current freestanding unit is, say, a 150sqm size just make sure you get 200sqm size for your inbuilt, although the one you are looking at I'm sure is around 250sqm from memory. They're not trying to sell you a zero clearance kit I hope!
As PeterB-CV8 said, one with an inbuilt fan will help warm the house up faster. Once it's warm it isn't really necessary. Of course, if you have reversible ceiling fans you are even better off.
May I ask why you've chosen the Regency - you don't have to tell me.
Mcnews, most slow combustion heaters have the ability to have a wetback fitted for water heating. We used to do a lot of solar/wood heating combos.