No issue at all, fits in my 1999 (NB) Miata
356099
Fits no problem in my 99 miata.  People have commented already about modifying slightly the vent tubes.  Mine were already modified as this is the third battery in my Miata (not bad for a 15 yo car) Previous battery was a WestCo that has been in place since 2008.  My Miata was cranking slowly lately and decided it was time to replace it.  The Marathon Battery was slightly less expensive and I thought I'd give it a whirl as it seems to get positive reviews.  The battery arrived in two days and it was charged, ready to install. The packaging was very secure (see photo) and the battery itself was in perfect condition.
1415273
Fit as advertised.  No problems with install.
4213115
It fitted perfectly on my Mazda Miata 1994. Just removed the old worn one, and  replace it with this one. Strong rubber with integrated washers, just like the original.
2668670
Same fit, as what I had in FX5. No issue what's so ever.
1623230
Fits as described. Haven't had a single problem yet. I put it in a 2011 Subaru Legacy and have no complaints.
2710184
I have no issues with this part. It fits just fine in my 2005 Dodge Ram 1500 with the Hemi engine.
1317490
fits exactly.  works smoothly.  No problems with connectors etc.
1686532
Purchased and arrived in good time / no damage to box or radiator during shipping.  A few screws later and I had the old radiator out of my 2003 Nissan Maxima GLE (automatic tranny).
The only possible knock / down grade I'd considered is the mounting screws/bolts at the top.  The nuts for the bolts are square and housed in a plastic casing at the top of the radiator.  They're easy to fish out if needed.  I had to get them out because the factory bolts didn't match the nuts that came w/ the radiator (and this didn't come with the bolts - just the nuts).  It was a simple fix:  Just swapped out the nuts for somehting I had around the house, but would've preferred that they matched up..  Also,  If you put too much torque while screwing the bolts in you'll strip the plastic casing that holds the nuts/bolts.  minor word of caution.
I'm perfectly satisfied and have put a few hundred miles on it without any issues.
4840676
Good fit on my 1993 Miata NA. The finish as it comes is good although some of the molding marks appreciate a quick once over with a sharp knife.

Overall excellent and i really like the difference it makes to a stock Miata. 4 Stars as it's not perfect, but it is very good.
3826520
so far no issues, fits as described! Although its clocked differently than my oem's but it isn't a big deal.
1392981
Fits my 2015 370z NISMO  perfectly. No issues to report.
1284962
Fit in my 2011mac mini, no issues, works perfect
1539892
fits great and works fine. No issues installing it
3884468
Excellent fit into 1997 NA Miata. Didn't use the seals that came with it, ordered higher quality ones instead.
Sound is slightly different than the stock unit, no big deal though.
Unit is physically smaller than OEM (See pictures).
No issues with CEL after installation.
Would recommend.
1031966
I just bought a 2006 Miata and installed this in less than three minutes. You do have to turn the head unit and your source device up (a Samsung phone in my case) and there is a bit of interference but otherwise the sound quality is decent and it works as advertised. A ground loop filter would take care of the barely audible noise.

Overall an excellent buy.
332380
Not much to say, fit my V6 2.5l 2001 kia optima, doesn't squeak, been running for a year no problems!
2774767
Fast shipping, easy install into an aftermarket aluminum miata radiator, had to run the fans in parallel to get good flow. Overall very pleased.