Yes, I use this too. Not only is everything you say true, this app is freeware and is supported extremely well. And for those of you, like myself, who have felt a little too "geeky" using a PDA shopping (stylus to check off items, etc), with a Tungsten palm and 5 way navigator button, handyshopper offers a "one hand mode" which allows you to do virtually everything with (as the name implies) one hand!
I've been an HS2 user for years now, and have created a long grocery list with things that actually apply to my family. My wife and I used to walk around Costco, each carrying our own Palms, and then would beam our checked items back and forth.
Specific to GTD, I have my weekly review checklist (as well as others) all in HS2 -- I simply took the list off the website and created the checklist. I added the additional stuff as a note -- so I have DA's full explination available and check-off-able. I also have checklists of my daily tasks (repeating) as well as lists of of tourist-worthy places (organized by town [Stores] and type, like restaurant, museum, historical [aisles]), which makes it easy to answer the "so what should we do while we're here?" question when people are visiting.
Basically, I use the built-in ToDo app or ShadowPlan for non-repeating items, and HandyShopper for all regular or semi-regular checklists. Checklists is a lightly-covered but critical aspect of GTD, for which I'm grateful for HS2.
I had no idea how dependant I was on HS until I busted my IIIc a year ago. Replaced it with an IPAQ then replaced that a month later with a Palm 510m because I couldn't find a HS app for the IPAQ. I use it for the usual shopping, but I also have lists for weekend chores (I'm active duty military so everything gets crammed into weekends), books I plan on reading and all kinds of other stuff. Best thing I've ever gotten for free. The second best is the TODAY app that replicates the PPC opening screen.