[Sci-Fi]

It's hard to say when it is time to change the shocks because it just varies by either mileage or is affected by the road and environmental conditions one faces on a daily or seasonal basis. A car owner has to check/inspect their shocks every now and then and decide when it's time to change them or just wants to change/upgrade the OEM shocks for better control/handling/ride characteristics.

Monroe Sensatrac (soon to be replaced by Monroe Reflex)and Gabriel Ultra Shock are both a twin tube, low pressure gas design (soft/medium valving) that is good for a daily driver and an upgrade to the OEM shocks. Replacement under warranty may be easier with these shocks since they are available nationally at most outlets.

The other gas shocks listed (KYB, Sach, Tokico, etc) are a mixture of twin tube (usually the front struts) and monotube (rear shocks), high pressure gas designs. Initially, your ride will be a bit more bouncy, but after a break-in period, the shocks will settle down and you should have a good ride and control. These shocks are better for more spirited driving and/or if your daily drive includes a lot of curves and tight turns (control is more important then ride qualities under those conditions...i.e. live in the mountains/hills).

Pricewise, with the exception of Koni, all the shocks/struts are priced about the same, so it becomes a personal decision which brand best meets your needs. The monotube design is more expensive to manufacture and the more modern design, so it is a bit surprising that the price would be so close to the twin tube designs. Longevity may vary by make too and like the OEM shocks, the road and environmental conditions will affect shock life, so YMMV.

Hope this helps and thanks for the complement.