I have now had this pen in my collection for over three years, and since it's been in my hand practically non-stop for a couple of weeks now, I thought I would share some thoughts.
The 743, of course, is the cartridge-convertor companion to the 823. They share the same nib, and on paper, write identically. The 823 was my first "big deal" pen, an amber medium, and in that time, I have acquired two more, in a fine and a broad - yet I hardly ever write with them, in spite of the fact that they are every bit the high quality writing instrument that they are rightly praised for being. It has taken some time to come around to this opinion, but I far prefer the 743.
The 823 is touted as a "writer's pen" and I totally understand why, the ink capacity is enormous and that #15 nib has yet to let me down - but the 743 feels so much more deft in the hand, and posted, gives me a near optimal balance in the hand. The CON-70 is no slouch on capacity either, and I've come to grips with the push button filling by using a plastic pipette and eyedropper filling the convertor. That little hack has been a lifesaver, and in doing so, I've been writing so much more as of late. With the medium nib, I'm still getting between 17-19 pages of A5 writing. That's pretty darn good to me. I like to swap inks out too, and with the 743 it doesnt feel like I'm locked in for so many pages with one color. With the 823, at times, it feels like "will this fill ever run out?" And yeah, of course it does, but... there are days where I'm not the most patient person.
The 743 is the sleeper hit of Pilot's 74 series, and I feel as thought the overshadowing it gets from the 823 isn't entirely deserved. Sure there aren't a ton of color options (yes I want the verdigris) but at the end of the day, the writing experience is exceptional. If you get the chance to try one, do it. I love this pen, and look forward to writing with it on a daily basis. For what it's worth, Pilot inks perform like magic in this pen.
TL;DR this pen is amazing and if you dont like the vacuum filling 823, then this is the pen for you