Is it true that using Robo advisor in a long run will incur high charges and not be able to take advantage in a long run?

As your Assets Under Management (AUM) grows, so does your management fee but do note that your dividends will increase as well. End of the day, it depends on your investment approach whether you want to rely on Robo to manage your investment or use Regular Savings Plan, or DIY.

It is true that robo advisor charges a continuous management fees based on % of AUM, but so are all professionally managed products (ETFs, unit trusts, managed accounts, ILPs, etc). What you want to pay attention to is their performance after net off all fees.