I actually agree with the fact that Olli doesn't sound too much like Jon, especially in terms of his accent and phrasing. But like some others of you state when Jon's deteriorating state of vocals get discussed - live shows cover a lot more than YT videos.
When I find myself singing along I don't notice it that much at all. What's great about this band is that they can play all the songs in the original key and hearing Bon Jovi's best rock tunes with that amount of energy (and the high notes in Prayer + the screaming in Runaway) is just great. It's not that it replaces a show from the original, but it somehow reminds of what the original could do that is lost nowadays and therefore I like them so much. Plus they always hang around after each show and have long chats with the fans that came around to see them.
About their guitar player - no he definitely is no Richie and technically surely no Phil. But he's actually the one who has improved the most over the years and on good days (he also has his "sloppy-Richie-days") his phrasing and his licks are stunning as well. I remember hearing a Dry County rendition from them in 2012 which was so passionate and full of energy that it beat both Dry County performances I got from Bon Jovi in 2011 and 2013.

One of my favourites also was this acoustic medley, even though he messed up some lyrics: