I can't add anything to the advice already given by @Zoidburg, @Madmerv and @jc12 (good work guys).
But I can shed some light on Shield and GG Betaglucan.
Did you know the bulk of these products are made up of good ol Oats. The kind we eat for breakfast - quick oats, porridge, whatever you want to call it. It's all shredded up into powder, and they might add a bit of other vitamins or minerals, but it's just oats. If they didn't shred it up, you would realise it's oats, and question why you are paying $20 for 60g of oats.
If you want to try it out on the cheap, feed your shrimp oats, which you probably already have in the pantry. You can make it into powder so the smaller shrimps can get at it, or just drop it into the tank straight out of the packet.
In addition to bacteria in a bottle, there are some good ones out there - do your research. No harm in adding some while you are cycling the tank. It is most important to cycle your new tank until Ammonia and Nitrite read zero before adding any shrimp. Find out what your LFS sell and start a thread asking for opinions before buying.