I know a few guys who have them, but they fish them from the cockpit. I do have some thoughts and things for you to think about before adding one to see if it will benefit you or not before you make such an expense.
First thing is I'm assuming your going after bluefin tuna if your considering one of these, other then bluefin, there is no tuna out there that needs this to be landed, possibly bigger big eye tuna but they are hard to soley target, and even large west coast yellowfin would not really warrant the need for this.
Your biggest concerns are with mounting, a simple thru bolt will not do, you need a mounting plate, at the least, personally I'd have a mounting plate welded to the anchor tie off in the anchor locker and then thru bolt to that, only way this structure can really tangle with large fish and be safe.
From a fishing stand point, I would personally HATE fighting a fish off the bow of any walkaround, first thing is footing, you have a shallow walk way to support you on a rolling boat, granted the post will support the rod mostly but you really cannot get a lot of leverage on the fish since you only use your arms. You would be better off using a full harnass from the cockpit, would allow the angler to use his or her body weight to gain line, as opposed to just your biceps with the post. Also, an angler with sound footing is a safe one in the cockpit, you have toe kicks to lock your feet when a fish surges and a place for your thighs to rest if the boat tosses. also, how would you land a big tuna on the bow, realistically you would need to poon it, but then you have a long line, longer then most captains would perfer for the job to tame the fish. Gaffing a tuna off the bow would be nuts, and I would strongly discourage it. Walking the rod aft with a big fish on is more dangerous then anything else and not suggested either. The other thought is are you fishing from the bow, or walking the rod forward once hooked. I'm not sure if you've hooked large tuna, but once hooked the last thing you would want to do is walk forward on a tiny walkway. I've tangled with numerous tuna to 200lb off NJ and Md, and lost as well as landed a few 500+lb bluefin at the off Md, having one hooked is an experience in itself. Holding onto a rod with a fish this size is a task in itself. Stand up gear, although not ideal will work on these fish, key is to change out anglers every 15 min or so and keep going in a circle through the guys until the fish is close, this keeps fresh guys on the rod. Also, have a mate saver vest and attach a line to the angler to the boat, this is a MUST when fishing for big tuna. Also, rod always stays attached to the boat as well, the more safety the better, especially if you have a guy attached to the rod which you will. With a big tuna, your going to have big drag settings, if you do not you will never stop it, and lowering the drag to get to the bow safely is really not an option, lower the drag and your spooled before you knew it, keep it tight and you risk someone going overboard. The best option is a chair, or fighting the fish from the rod holder when possible, although a Grady would need many mods to accomodate swivel mount rod holders to do the job as well as backing plates, and ideally a plate attaching the plate to the hull somehow. On big sportfishermen there is about 1.5" of solid glass where these rod holders go, on commercial boats they have the same, or often a metal brace attaching it to the hull.
If you were on a center console where walking forward with a hooked fish is much safer, using one of these posts would make more sense and be a lot safer, but still your at a disadvantage to the fish using one. The only main advantage really is if you have back problems and do not want to apply that much pressure to a fish physically, but then you better have arms of steel. You can use a bucket sytle seat to gain leverage with the post, but personally on a walkaround that is danergous to me, if you loose your balance you have no high rails or gunnels to go against, and will fall. Also, you will not have a place to comfortably stand and apply this type of pressure and feel comfortable.
I know the post looks like a good idea, and for some it works well, but in your situation I do not see much of a benfit for its use, and the benefits it does have are simply outweighed by dangerous situations to be able to take advantage of the posts usage.
In essence, on any outboard boat with a big fish hooked you will follow it regardless, following a fish from the bow vs the cockpit is not much different, you can gain line just as fast but the cockpit is safer. Also gives your hook a better angle, a 45 to the fish is better then following from behind where you could unhook the fish if it surges forward, and big tuna will. I would rather fight the fish from the cockpit with the rigger up and chase it that way, no running around for the angler whether he is fishing stand up or from a post. The post might be a more viable idea in the cockpit, just cover the holes with a plate when not in use and then attach it when using it, would give you better piece of mind if you thing the post is better for you to fight from, and would be much safer too.
Think about all that I've stated, personally I would not want to ever battle a big tuna from the bow of a walkaround, hopefully my reasoning hits home and keeps you guys safe, if you still think it will benefit you then go for it, but atleast then you've thought out all the possibilities.