Depends. If you just sharpen knives, NO scissors, planer blades, chisels then the Apex may well be all you need. The Apex is available from a LOT of dealers, jobbers, and via ebay etc. The Pro is only available from EdgePro. It's serial numbered signed and your name goes on it. Personally even if I was getting the Apex I'd buy direct from EdgePro even if I was paying a bit more. The customer service is fantastic and the guarantee is great. If you want the scissors, planer blades and chisels sharp you have to get the Professional version and the additional attachment at 95$ or buy the complete kit # 3. 485$ USD
No you aren't stuck with just stones from EdgePro. However if you want stones that have been tried, tested, and are totally consistent with the EdgePro then get them from EdgePro. 1x6 stones are available from a lot of tool and die makers suppliers and most large abrasives dealers.
If you sharpen massive recurves or hawkbills get the 1/2 wide stone, it's only available in the 320grit however. Get extra 120 grit stones they wear fast I get just the stones 4 at a time and mount them on the blank myself. Get a spare 220MF and 320EF as well. The 600 ultra fine you won't wear out for about 10K knives or more. If you drop a stone in the sink or on the floor you can break it. I know I've done both.
Get the silicone carbide for lapping your stones. (You'll have to get your own piece of glass to use it on, I used a square piece from a coffee table for a long time. Now using a 14x14 piece cut from glass from a light table) Get the full range of polishing tapes 12µ, 3µ, 1µ, and 0.5µ get polishing blanks for them all saves having to peel off tapes and apply the next size.
A fair number of users are going to diamond from EZE-Lap, order the 42 series without the pedestal in coarse, medium and fine and attach them to your own stone blanks. (Note the stone blanks and the tape polishing blanks are different) I have the EZE-Lap Diamonds but I'm not thrilled with them but it may be that I haven't used them enough to break them in. I can see the point of not having to use water etc but personally I haven't had as good an experience as I have with the EdgePro stones. Also the diamonds do require a lighter touch in my opinion. But then maybe that's why I haven't had much luck with them.
1. I'd order from EdgePro. You can't beat the service or support.
2. Get extra coarse stones they do wear fast get 3 spares at least if you do a lot of reprofilling. Get a spare 220MF and a 320EF stone with your order.
3. Get all the polishing tapes and blanks for them.
4. Get the silicone carbide for flattening your stones.
5. Get a piece of glass for # 4. Flatten your stones regularly they will last longer and work better.
6. Go to your local hardware store and buy a 2" wide roll of painters tape. this will be used to protect the blade table, provide stability and to tape the edges of knives to prevent scratching, especially import with the 120grit stone.
7. Practice on larger knives with decent steel first, with good flat surfaces till you get used to holding the knife steady.
Enjoy the sharpest knives on your block.