Should a candidate interested in studying finance and economics join the ABM course at IIM Lucknow?

I think the PGP course is a better option if you are interested in Finance and Economics. This is because the ABM program offers the choice of only one option during the second year. The electives of the first year of both the programs ABM and PGP are the same. They comprise important topics like Micro and Macroeconomics, Financial Reporting and Accounting, Managerial Accounting, and Financial Management.

Most importantly you will be missing out on Finance and Economics courses. Some ABM students are diligent enough to sit through these classes despite everything.

There are no major differences in the placement scenario of ABM and PGP. Though I will recommend you go for the PGP program of a more reputed institute. Through ABM you will have to resort to self-learning more.