Featured Application: This compact but precision highly stable NMR time-domain relaxation spectrometer is most useful for quantitative material science measurements of both the mass and the mobility/dynamics/stiffness/viscosity/rigidity of hydrocarbons and polymers, both in the bulk and in sub-nano-meter and upward sized pores. It is highly useful for studying the properties of hydrocarbons in pores in applications such as recovered porous rock samples from oil reservoirs, and in fired biochar porous carbon samples, to give just two examples. In addition, applicable to both these fields of study is the ability to make NMR Cryoporometric measurements of pore-size distributions in porous materials, for sub-nano- to over micrometer sized pores. NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly available compact NMR time-domain relaxation spectrometer, the Lab-Tools Mk3 NMR Relaxometer & Cryoporometer [Lab-Tools (nano-science), Ramsgate, Kent, UK (2019)]. Being Field Programmable Gate Array based means that it is unusually compact, which makes it particularly suitable for the lab bench-top, in the field and also mobile use. Its use with a variable-temperature NMR probe such as the Lab-Tools Peltier thermo-electrically cooled variable-temperature (V-T) probe is also discussed. This enables the NMRC measurement of pore-size distributions in porous materials, from sub-nano- to over 1 micron sized pores. These techniques are suitable for a wide range of porous materials and also polymers. This instrument comes with a Graphical User Interface (GUI) for control, which also enables both online and offline analysis of the measured data. This makes it is easy to use for material science studies both in the field and in university, research institute, company and even school laboratories. The Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry, particularly near the probe liquid bulk melting point. Results from example NMR Relaxation and NMR Cryoporometric measurements are given. [ABSTRACT FROM AUTHOR]