The 3 in 1 machine is a dated design compared to what has been available for quite a few years.
It had been around for some time before I bought my new lathe in 2003.
Machine Mart and Chester seem to be the only suppliers in UK.
A friend has one, and have had to help him out with the odd problem, to improve the machine. Also a 4 jaw chuck for one is more expensive compared to a 4 jaw for most other machines. The chuck fitting is unusual compared to other machines, which probably accounts for higher price.
Other machines can offer a wider range of accessories, should you need them.
It depends on how wide is the range of work that you plan to do.
Milling is a process that requires rigidity. (it is effectively, a series of interrupted cuts ) In my book a 3 in 1 machine does not offer greater rigidity, or as much, as a dedicated Mill or Mill/Drill.
The Cross Slide is effectively the X axis of the mill, with the travel along the bed the Y axis, and is limited compared to that of a conventional Milling machine.
Having said that, if you are prepared to accept limitations and compromises, you might find that it does all that you want.
As always, you pays your money and makes your choice.
Howard