How big of a difference is there between a pressurised and non-pressurised portafilter? I have been trouble shooting some of my own espresso and realised that my lower-end machine might just be unable to make a better shot due to having a pressurised portafilter. So with that I wanted to find out what real differences having an unpressurised portafilter there are compared with a pressurised one.

For those interested, my current espresso problems are as follows:

I manage to get the grind to a size where I'm noticing good thin mouse tail pours but the lack of thick, golden brown crema makes me think I can get a better shot.

I've read that light coloured crema or thin crema is a symptom of underextraction, depending on the length of the shot (where mine was in and around 20 seconds for a double shot, so relatively fast). I then ground finer and the extraction immediately changed. The mouse tails disappeared and the extraction was fast, almost instantly blonding within a second of the extraction. Liquid was not pouring out extremely fast but in comparison with the slower previous extraction it was relatively fast. I tried to continue to lower the grind size to attempt to slow the extraction but to no avail.

Could this be a problem with the pressurised portafilter?
Pressurized portafilters either restrict water flow or require a certain buildup of pressure before the espresso spills out the bottom of the portafilter. 

So there are several problems with that taste-wise in espresso. The resistance is now not in the ground coffee itself, but below it. Additionally, if your coffee is ground finely and uniformly in a good espresso grinder (as one would for a non-pressurized portafilter), this sort of portafilter will result in too much resistance and thus a slow, over-extracted shot. It can also make your crema look a bit odd because it can emulsify some of the oils in your extracted shot (depending on the design of the specific portafilter).

Essentially the requisite grind size to produce acceptable espresso using a pressurized portafilter is much larger than that of optimal or delicious espresso.

This sort of portafilter does have its upsides, though. If you don't have access to a quality espresso grinder, and you are using either store-ground beans or imprecisely/more coarsely ground beans, a pressurized portafilter can make acceptable espresso from them whereas the results in a standard portafilter would be very watery and underextracted.