FLR M visa postal or appointment application

My Visa entry clearance visa is about to expire on 6/05/2016. The Gov website just says apply before your visa expires.

I am thinking which is best option for me to apply for the FLR M visa. I am no rush and don't really need my passport for next few months, but want to know if I have submitted my application via post this month and I do not get my passport with the FLR M visa stamped until 06/05/2016. What are the implication, wiil I be breaching any laws?

Do you recommend I go for the same day appointment application? I know it costs £500 extra.

If you apply before you visa expires, your existing visa conditions continue while HO is processing your application, so no, you will not be an overstayer or breaching any laws/rules.

Thanks for replying so quickly and clarifying this for me.