I'm assuming you're talking about dirt because I don't think fox farm makes hydro food (I could be wrong). In regards to H&G, I'm currently testing their hydro food Aqua Flakes and to give you a little insight into the company, their Aqua Flakes product is solid. Unfortunately the pH isn't but it's a high quality plant food that's as cheap to run as DynaGro (assuming you don't buy into H&G's additives which aren't needed).
I don't think you can 'ease in' as their bases are usually split into 2 parts and the quality of the base will tell you a lot about whether you want to try anything else from the company. I'd suggest you buy a litre of the two parts you'll need and see if it works for you. Personally, I wouldn't mix the two lineups for no other reason than to keep things simple and see if you like working with H&G.
I just wanted to comment on this statement real quick. It's very rare that a hydro shop owner would steer you in a certain direction based on results rather than profit. In the case of H&G vs Fox Farm, I'd be willing to bet that H&G is more cost-effective (base nutes only) but that's just based on the concentration levels of other similar products that I've used. That being said, it's generally beneficial to ignore anything and everything a shop owner has to say. Get your info from talented growers across a few different forums and make a truly informed decision the next time you walk into your local shop.I have been talking to some guys at local hydro shops and feel like I want to switch to something better.