I personally can't see what the advantage is as you have a reasonable
number of curves to choose but they may not necessarily be what you need
for your engine even the minimania settings page
(http://www.minimania.com/web/DisplayID/1792/SCatagory/ELECTRICAL/DisplayType/Tec
hnical%20Information/ArticleV.cfm)
say that they can't provide the advance required for some of the engines
listed and as there are no modified engines the exact requirements are
already known. I presume you may be lucky and need one of the standard
curves on your modified engine.

Alternatively if you are modifying you will be sticking it on a good
rolling road anyway. They will tell you what curve you need and then
they or you can set up your distributor to match. You will also get your
fuelling spot on at the same time.

Presumably the 123 will come into their own when the various standard
fit distributors are no longer available.

Peter