Check out the Beretta forum for more responses.
Some swear by their SP products, others find them unneeded. Its up to the user to decide if they are worth it. The trigger is a popular upgrade. But honestly while I have considered it for years I have also resisted it for years due to the cost. I have the DIY trigger upgrade and it is OK. Not great, not bad, but OK. The price was right and it took all of 10 or 15 minutes to do.
They make other parts too like the stainless steel recoil spring guide and a special buffer. Some will lead you to believe the factory plastic guide is just positively going to break. Well, maybe so but since getting mine back around 2004 or so its still has the original and it hasn't been a problem. If you just have to have accessories on and in your rifle and you have the money, by all means help enrich the guy who makes this stuff. If you just want a good carbine that works and you want to save your money for ammo, go the DIY route. Ether way you will be OK.