For experienced pilots, there is a benefit in experiencing different types of aircraft, including microlights, if they choose. However, I suggest that new candidate pilots will learn flying with more long term value in a certified airplane. With those skills, you can then decide what aircraft type more suits your flying desire. There are certainly some important flying skills which cannot be flown nor trained in microlights.
Avoid thinking of the PPL as your goal. Your goal is to fly, the PPL is just a step along the way. It's not as though you plan to earn your PPL, then stop flying, right? Have a longer term flying strategy (and budget), and you'll worry less about the cost. If you have just enough money to get to the PPL, you could become quite disappointed when you get there. Either you really want to fly more, and the budget is not there, or you're not so keen on flying after all, so why are you there? Think beyond the PPL....