Could someone tell me roughly how many pounds does the B510, B530 or B540 weigh? I'm thinking this may solve our travel dilemma for our big May trip (which will include a cruise). DS1 (will be 5 then; currently around 43 or 44 lbs) uses a Regent at home. We usually use our Radian for his travel car seat, but we plan to use the Radian for DS2 (who will be 23 months) for that trip instead of bringing the Roundabout (because the slimmer profile is easier for deal with). I hate the idea of giving up a 5 point harness, and considered the travel vest that folks have mentioned here, but that vest makes me way too nervous. I just can't believe the vest would be safer than the Compass (or Graco Turbobooster) with the regular car seatbelt, but maybe that is just a mental thing. I can't imagine not having something surrounding his head and sides in some way! But if the 5 pt harness travel vest is truly "just as safe" as one of these portable highback booster seats, please let me know as then I'll reconsider.
Edited to add: oops, I just noticed this thread is in the Chat forum. Please let me know if I should repost my questions in the main car seat forum. Sorry about going off topic!