As a provider should I purchase a monthly membership?

Can't you get a free one?

So it depends on what you want out of your membership.

I believe you need two reviews to get a lifetime membership

Once you have a review, if you link your review profile to your username, you will have "free Limited Provider VIP" which gives you access to your reviews, whitelisting, and the PM system. If you purchase full VIP, it will give you access to all reviews and more search functions. Some ladies use that as part of their screening, and some just consider it part of the cost of doing business. Others are content with the Limited Provider VIP. You nedd to decide for yourself what works for you , but I would assume at least until you qualify for The Free provider VIP, it might be worth paying for VIP at least for a month.

For a provider, one review gets her Free Linited Provider VIP membership, if she asks for her reviews to be linked to her username. Limited provider VIP is not quite the same as full paid VIP
For  a hobbyist, 2 reviews gives him/her 30 days VIP membership.

I agree, that a great screening tool, is seeing how a potential customer reviews others. You can get a better idea about what interests the client and what are their turn-offs. So FULL VIP is the way to go.  

Of course some providers don't really care and would prefer to find out what each customer desires on their own