If I purchase stocks via DBS Vickers (Cash Upfront), may I use FSM One to sell the stocks? Are there any disadvantages (monthly/yearly charges by FSM One)?

There are no disadvantages if you sell via fsmone!

Personally for all my sg stocks I purchase with dbs vickers cash upfront and sell via fsmone! The commission for selling via fsmone (flat fee $10 excluding gst and clearing charge which adds up to about $12) is much lower than dbsvickers (Minimum $25)

I tried selling via DBS vickers before and had some issues due to my selling limits so it is important to check ur selling limit on DBS vickers! Fsmone gives u a default $50k sgd selling limit for cdp.

If you would like to sell via fsmone do note that you would have to do a linkage of ur cdp acc and fsmone acc by filling up a form and mailing it to fsmone