The 'buy your own type rating" is of course up to the individual as to whether it is worth the risk. It may well increase you chances of getting a job - or maybe not.
Imagine you have just forked out 15-18k on a posh new Airbus 320 or Boeing 737NG type rating, you nip down to WH Smiths on the Wednesday morning, buy your copy of Flight International, turn to the back pages and there is a slew of adverts from regional Turboprop operators, desperate to take on low houred pilots. You send off your cv and you get rejected, not even invited to interview. Why would this be? You have a posh jet on your licence, thats why.
Having an medium range jet type on your licence limits your choice of jobs that you can apply for, smaller operators with turboprop fleets or commuter jets will look at your licence and assume you are going to disappear off to the likes of Easyjet, Ryanair, BMI etc etc as soon as the chance presents itself.
If you have the financial wherewithall to dispose of another 15-18k on top of the 50-80k you have already spent on gettting a CPL/IR/MCC then I guess it is not a problem, but if you have to borrow yet more money to fund a type rating, think long and hard about this course of action. If you don't have a job lined up at the end of the course a Type Rating with very few hours may work against you instead of in your favour.