If the online booking tool gets to the payment screen with the flights you wanted, then it will work.

The tool only shows flights which have availability in the applicable fare classes (for the most part, L, D and A with I, J, W, Y, Z, H, T, R and E for selected routes/situations) at the time you look up the flight. It will then check that fare class is still available when you reload a saved plan or move through the payment and booking screens. eg, if I'm looking at a DONE3 for LHR-DXB. It will look up the 5 oneworld flights on that route (3 BA, 2 QF) and the codeshares (AA, IB, MH on the BA flights) and only show those flight numbers with D availability. It will then list anything with L, but no D followed by available connections (eg, LHR-DOH/AMM-DXB).

Prices can be annoying to find as it now requires access to a GDS look up tool (such as expertflyer) to get current base fares. Taxes can also make a ticket that looks cheap become much more expensive (eg, India/Sri Lanka base fares look good, until you add the Indian luxury taxes on D and AONEx's)

Yes, these are revenue tickets. However some agents don't seem to understand that. I had an issue on my last DONE3 where I was trying to change a AA coded, US operated flight. Between CX (ticket issuer), AA and US, they kept pushing me off to another airline until I spoke to some agents in person. AA staff at LAX, JFK and SFO were happy to make changes, could see availability, but couldn't make the actual change because it was sitting on the US system which they didn't have access to. When I spoke to US agents at LAS, they called their pricing and ticketing office who swore it was an award ticket. I finally managed to get CX UK to make the change when CX US refused to touch it ("we don't operate that flight, not our problem").

Since I started doing DONE3's, I've been starting in ICN or TYO. I'm based in CBR, so I've been using DAS13's (Circle Asia) to get from Australia to Tokyo/Korea and back. I've included some extra stops in Asia on that other ticket.
Depending on the route and exchange rates, I've been able to get a DONE3+DAS13 for less then an ex-AU DONE4.

I've had issues with the per continent flight limit in North American and Europe, so I've been getting flights to the nearest hub, then getting short haul 1ish hour flights on different tickets. Such as flying to ORD, then getting an extra return flight to STL, or into LAX with extra LAX-SFO-LAS-LAX flights. (tip: never to cross ticket connections with IB. It's just asking for baggage issues)

People try to avoid certain airlines due to high fees. Mainly BA who tends to charge their own fuel surcharges for other airlines flights. Ticket with BA and have BA put their surcharge on a MH coded, MH operated KUL-ICN...
One trip, I was able to save almost $1000 by using IB and MH codes on BA flights.