Hi Sam. Unfortunately I do not have the time to carry out the test with my current workload. I have tired all three with a DSLR and my findings as below. Hope it helps.
1. Bird is the easiest to fly properly (non tech, just from my feeling). Some designs require a heavier load to fly properly while some, do not. Bird does not have this prob as gimbal position can be lowered but only by a limited range.
2. Merlin is the lightest setup < BBIRD < GLIDECAM HD2000. Have not weighted it physically, just by feel so far. By comparison of the raw weight exc counterwieghts, the results are as above. But do not forget the design difference will play a part in how much counterbalance weight you require.
My take is, try out before you buy if possible. Cathay > Merlin, Expandore > Glidecam. Too bad no local dealers for the BBIRD. Anyway if it works for a price you like, its GOOD!
3. BBIRD + Glidecam HD + Merlin are all easily balanced. Handheld or with a docking stand as all comes with thumbscrew adjustment now. BBIRD has better quality screw compared to Glidecam. Merlin uses a long knuring instead of a thumbscrew.
4. BB comes with everything you need. Glidecam + Merlin requires some purchasing of optional parts. Eg: docking bracket (Glidecam + BBIRD).
5. Load: BBIRD 8Ibs max, 3.2kg cam was possible to be balanced and flown. Glidecam has 3 series, if compared to HD4000, BBIRD is much lighter but the HD4000 can handle up to 10Ibs. If compared to HD2000, HD2000 max load is lesser at 6Ibs but the total weight is slightly heavier (inc counterweights)
Why? Cuz the BBIRD has an extra inertia bar provided that helps a lot. The weights are moved further out from the post, doubling the inertia without add weights.
Merlin can handle up to 7Ibs. Sexiest of the 3 but it requires the most skill to handle. It works very well if balanced properly and it does not require a lot of weights to balance as some ppl mistaken.
Dun forget the load is inclusive of the counterweights so you have to divide by 2 and see if your cam fits in. At the end of the day, ask yourself what is the required and whether expansion is required for heavier cam. Its no point to cater for handheld up to 10pounds. Hands are not made of metal!
6. Clamp Mounting plate: Sucks on the BBIRD. Screw in to secure is slow. Need another QR adapter for sure. Merlin best, using a clamp plate and half clamp position prevents accidents of camera falling off. But you also need a quick release adapter if you ask me.
Glidecam plate has 4 thumbscrews to remove and no quick release tripod adapter. Need to remove camera from plate to mount on tripod or get another quick release adapter on top of it.
7. Build Quality: Merlin < BBIRD + Glidecam . Merlin looks and feel very pro. The other two does not look as pro.
8. Price: Glidecam < BBIRD < Merlin