The BH 300 is a multiple frequency machine (two frequencies, as I recall). I do own one, but don't use it all that often. It will get deep and it is waterproof to 25 feet. It was made for hunting in/around salt water. It is a heavy machine though and Whites no longer makes the model. You'd still get a 2 year warranty if you buy a new one that the dealer still has in stock. It would not be my choice for hunting a park - but I'm quite happy with its performance on the beach.
I tend to use my MMK when I hunt the beach, but I don't really hunt the beaches all that often. The MMK is much lighter in weight and it does a very good job at the beach. The MMK is waterproof as well - to a depth of 15 feet (I believe). The MMK has three frequencies - you select one of the three. It does quite well - much better than any other single frequency machine that I know of - in the salt water. It is a fantastic choice for park hunting and fresh water.
I don't own, nor have I used, the Minelab Equinox (I chose the MMK over the Nox and I'm pleased with my decision). The Nox (either version) is much lighter than the BH 300 and it operates on more frequencies. I'd take the Nox over the BH 300 for park hunting any day - simply due to the lighter weight and it should be (I'm assuming) easier to swing for longer periods of time.
All that said, the BH 300 is a very good machine and it would serve you very well for hunting wet sand and the water. You'll have to decide if the weight would be an issue for you (or not). I'd suggest that you go to a dealer and swing several machines: try as many out as you can and see which machine fits you best.
BTW - you can belt mount the control box of the BH 300. That would make it a very light weight machine. (I have not belt-mounted my BH 300).
There are other options you might wish to consider as well - PI machines are one example. You'll dig everything, but they'll go deep.
If you're talking about fresh water beaches, there's the AT Pro and the MX Sport from Whites. Neither is ideal for salt water, but both would serve you very well for fresh water and parks. I do own the MX Sport and am very happy with its abilities; it is fantastic choice for park hunting and fresh water (and it will do an ok job in wet salt sand conditions).
