Here's my last 3 years worth of 3-piece combo experience:
Combo WILL NOT:
1) It will not seal the cab from steady or heavy rain. Will keep most hail out of the cab
2) Will not be easy to fit. I can take just as long to put the entire 3-piece combo on as it does with the full factory top.
3) Will not make jeep secure from thieves.
Combo WILL:
1) Protect from wind etc. Sometimes it's just too windy/cold/annoying to drive topless. The jammer is not a full top but it almost feels like one.
2) Is very comfy driving with the tonneau, jammer and doors on with bikini/roof off. You can see the stars/sun and have little or no wind in the cab.
3) Is EXTREMELY quick to remove. It's a pain to put back on but it's very quick to rip off.
4) The 3-piece combo can fit into a backpack.
If you want to make the cab reasonably watertight with a jammer, either shove something into the gaps or use a SAFARI top. The BIKINI top only cover the front seat and accumulated rain runs off the back of the bikini top then onto the floor behind the front seats. The safari top drains the water onto the tonnea cover (assuming you've got a tonneau).
I went on a week-long trip with just the 3-piece combo. It was fine. It rained a fair bit on the last day i remained resonably dry. I've been on half a dozen camping trips with just the combo. Here's a pic up the beach: