There is a saying that once you get to orbit, you are half way to anywhere in the solar system. It is a saying that is based upon a spacecraft’s delta-v, the change in speed needed to get from one place in space to another. It sounds wrong, because getting to a 150 mile circular orbit around the Earth does not seem like half way to millions of miles of distance to Mars, Venus, or Mercury, and ten-minutes to orbit is not half the months needed to get to these destinations.

Even for the delta-v aspect the saying is an exaggeration, unless aerobraking is used with a planet’s atmosphere. However, Mercury does not have an atmosphere for using this tactic for navigation. Here is a chart with estimates of delta-v needed to navigate between various places in the solar system:
http://i.imgur.com/SqdzxzF.png

The chart shows an estimated delta-v of 9½ km/sec to get to low Earth orbit (LEO) but 11 km/sec to get from there to be captured by Mercury. That means that to get into a high orbit around Mercury, you would need a larger rocket to get from LEO to Mercury orbit than you could have used to get the probe into orbit around the Earth. So, to get to Mercury would require a launch vehicle that can lift a rocket into LEO that is more massive than one to launch the probe alone into LEO. To get to Mercury, the probe would have to be fairly small and limited in its abilities.

Commenter F, above, linked to an explanation of how the probe’s namesake, Giuseppe ‘Bepi’ Colombo, described another way to save propellant mass by using gravitational slingshot maneuvers to achieve much of the delta-v without using propellant, or not using much. That is the advantage, but the disadvantage is that it takes much longer to make these maneuvers than to navigate directly to Mercury via a Hohmann transfer orbit, as you propose.

If we have patience, then we can send a probe with more instrumentation to the places that we want to explore, replacing propellant with science.

https://behindtheblack.com/behind-the-black/points-of-information/scientists-rediscover-the-advantages-of-nuclear-power-for-moving-probes-through-the-solar-system/

https://www.esa.int/Science_Exploration/Space_Science/BepiColombo/Why_does_it_take_so_long_to_get_to_Mercury