The hike from the lake to the couloir is longer than it looks. It's just under 2000 feet of climbing so take it into consideration. Also, in some years there is a bergeschrund at the base which will need to be crossed or turned.
The route is often snow filled with usual alpine conditions, ie fluffy snow in winter, scree in summer, often AI in the fall. Be prepared for any combination of the above any time of the year. It's about 1500 feet of straightforward climbing. Sometimes there's a cornice a the top which you can go around (or though if you really wanted to).
I measured the elevation at the base/start of the St. Jean couloir (right where the bergshrund would be) at 12,250 feet. You top out of the couloir at ~ 13,500 feet.....that's 1250 ft of vertical.