Very good bikes, it's a shame they stopped making them.
What year are you looking at?
I've had one of every version, apart from the 650b one as they stopped making them! The Heckler 5 2002 to 2007 although now an old bike was very robust and mine just keep going and going, my brother rides it now. The Heckler 6 2007 to 2012 had some problems with the early swing arms cracking, I think they changed the design for 2011 onwards, the ones with pinch bolts around the bearings cracked when people tightened the bolts too much so watch out for that.
Climbing is good, I find the rear tends to feel tighter when peddling compared to a VPP design which seems more active. Weight wise their average, depends on build, Heckler 6's will take a 160mm Lyrik, always good to get good strong light wheels and it'll feel better. I've ridden all mine for xc on the South Downs, it's been to the Alps and a few trail centres in the UK. It's still my favourite bike. Only 2 bearings to change, very easy, but they seem to last for ages. A good all rounder I'd say.
Get a size up if you can on the older ones. good luck.
Excellent bike!!! I had a 2016 heckler and it was a good climber and could push way about her weight decenting. Sizing on those is on the small size, so be aware. Fun bike, that was such a good entry level bike, I can’t still figure out way they stop making it. Glad I had one
Another vote for a great bike. I have a 2014 which is the first year it was offered in 27.5. At the time it was marketed as the "poor man's Bronson" and I would say that was a good description. It won't climb like my since upgraded to 5010 but its not too far behind. Mine's been used and abused but still a solid back up bike.
I had a 2012 or 13 Heckler and loved it. It pedals up hill pretty good and was fun on the down hills. I gave that to my son when I got a new bike two years ago and it is still going strong for him. Its a fun bike!