I haven't heard the Plop-in-the-box with the BG planar tweeter, but I can't imagine it would be bad. Before building it, you should ask Dennis Murphy what his opinion of it is now, as it is an older design.
I've built or heard 2-way speakers with that same M130 woofer and three different tweeters:
- MBOW1 with the OW1 ¾" dome
- MB27 with the Seas 27TFFC 1" dome
- MB20 with the Morel MDT20 1" dome (this tweeter is no longer made)
All are very good speakers.
