My next project is around IR circuits so i was thinking of getting a multimeter with a frequency function. Is this function any use and how does this differ from a o-scope?
A multimeter will give a digital readout of the frequency only. An o-scope shows a picture of the waveform (from which you can derive the frequency from the waverform period). An o-scope is a much more versitile instrument than a multimeter (and generally considerably more expensive). Many digital o-scopes also give a digital readout of the frequency.
Also, most DMMs bandwidth is quite small compared to most o-scopes on the market. For instance, my Meterman 37XR as a bandwidth of 10MHz, priced for around $125.00. You can by a scope with 10Mhz bandwidth fairly cheap in todays market and still get the benefit of analyzing the waveform. You don't get this with a DMM unless it has an LCD screen, it which case you might as well use a scope for the price you would pay. Depending on the type of work you are doing and the clock speeds involved will determine the bandwidth of the scope that you need. But I would definitely use a scope versus a multi-meter for measuring frequency because of the added visual benefit. Unless you don't care what the signal looks like