I own a Bonneville. I believe that it is suitable for a first bike with a little common sense when starting. The Bonneville has these points in its favor:
-very compact frame for an 800cc, feels lighter than its weight
-low center of gravity
-steers very easily
-docile handling, handles very predictably, leans easily
-very flat power curve, no hot spots, no surprises
-throttle very easy to modulate
-torquey, won't punish you for being in the wrong gear at the wrong time
-basic design, easy to maintain. Also easy to mod.
-rugged engine and transmission, not easy to kill
disadvantages:
-brakes could be stronger (of course they won't surprise you, the issue is whether they'll
stop you at all!!

)
-narrow tires fairly sensitive to pavement grooves, bridge grates, etc.
-more sensitive to wind gusts than some other bikes
-transmission can get "moody" when hot, neutral sometimes runs away and hides (hey, it's an English bike, it's gotta have some eccentricities!)
I believe the 62hp spec is over-stated for the Bonneville in stock form. With mods, it will get 62hp and more, which transforms the character of the bike. But in stock form, it's a bit of a pussycat.
We also own a Suzuki Marauder 800, which weighs the same as the Bonneville, has a similar size engine, but on paper makes less horsepower (44 vs. 62). I have sometimes seen the Marauder approved as a beginner ride on this forum. Owning both, I would not hesitate for a second to recommend the Bonneville over the Marauder as a beginner bike, based on its docile and predictable handling. For a newbie, the Marauder can be a pig at low speeds. On the other hand, the Bonneville goes around pylons like a 250cc bike - it's so easy, it feels like cheating!