Well somewhat.That excursion minimum gets moved down to where there is little energy coming below the port tuning so yeah-though now with the port effect moved to a lower frequency there will be more midbass excursion. Still likely better than something tuned up like to 70 Hz, where any low bass gets into that region where the port unloads the woofer which goes nuts.
A first order filter won't be as effective as a second order, but yes easier to make. If you plug the port, the box becomes second order, total 3rd order with a highpass capacitor.
Harrison Labs are good for what they are, though the frequencies are off. My "100 Hz" were -6 dB at 100, -3 dB at 70 and 155 lowpass and highpass. I'd get this one because it is more flexible and barely more expensive
http://www.hlabs.com/products/crossovers/index_files/Page384.htm
or perhaps better there are some inexpensive Rolls active models (search "rolls crossover")
Oh, I almost forgot to rant how STUPID it is that 2-channel equipment rarely has a highpass filter, and double public caning and tarring and feathering on those that have a "subwoofer" output with no highpass.